Exar

Corporation 48720 Kato Road, Fremont CA, 94538

(510) 668-7000

FAX (510) 668-7017

www.exar.com

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

AUGUST 2004

REV. 1.2.0

GENERAL DESCRIPTION

The XR16L2752

(2752) is a low voltage dual

universal asynchronous receiver and transmitter
(UART) with 5 Volt tolerant inputs. The device
operates from 2.25 to 5.5 Volt supply range and is
pin-to-pin compatible to Exar's ST16C2552 and
XR16C2852. The 2752 register set is compatible to
the ST16C2552 and the XR16C2852 enhanced
features. It supports the Exar's enhanced features of
64 bytes of TX and RX FIFOs, programmable FIFO
trigger level and FIFO level counters, automatic
hardware (RTS/CTS) and software flow control,
automatic RS-485 half duplex direction control output
and a complete modem interface. Onboard registers
provide the user with operational status and data
error flags. An internal loopback capability allows
system diagnostics. Independent programmable
baud rate generators are provided in each channel to
select data rates up to 6.25 Mbps at 5 Volt and 8X
sampling. The 2752 is available in the 44-pin PLCC
package.

OTE

1 Covered by U.S. Patent #5,649,122 and #5,949,787

APPLICATIONS

Portable Appliances

Telecommunication Network Routers

Ethernet Network Routers

Cellular Data Devices

Factory Automation and Process Controls

FEATURES

2.25 to 5.5 Volt Operation

5 Volt Tolerant Inputs

Pin-to-pin compatible to Exar's ST16C2552 and
XR16C2852

Larger FIFO version of PC16C552

Two independent UART channels

Reg set compatible to 16C2552 and 16C2852

Up to 6.25 Mbps at 5 Volt, 4 Mbps at 3.3 Volt
and 3 Mbps at 2.5 Volt with 8X sampling rate

Transmit and Receive FIFOs of 64 bytes

Programmable TX and RX FIFO Trigger Levels

Transmit and Receive FIFO Level Counters

Automatic Hardware (RTS/CTS) Flow Control

Selectable Auto RTS Flow Control Hysteresis

Automatic Software (Xon/Xoff) Flow Control

Automatic RS-485 Half-duplex Direction
Control Output via RTS#

Wireless Infrared (IrDA 1.0) Encoder/Decoder

Automatic sleep mode

Full modem interface

Alternate Function Register

Device Identification and Revision

Crystal oscillator or external clock input

Industrial and commercial temperature ranges

44-PLCC package

IGURE

1. XR16L2752 B

LOCK

IAGRAM

MFA#

(OP2A#,

BAUDOUTA#, or

RXRDYA#)

MFB#

(OP2B#,

BAUDOUTB#, or

RXRDYB#)

XTAL1
XTAL2

Crystal Osc/Buffer

TXA (or TXIRA)

8-bit Data

Bus

Interface

UART Channel A

64 Byte TX FIFO

64 Byte RX FIFO

BRG

ENDEC

TX & RX

UART

Regs

2.25 V to 5.5 V VCC
GND

*5 Volt Tolerant Inputs

(Except External Clock Input)

2752BLK

UART Channel B

(same as Channel A)

A2:A0

D7:D0

CS#

CHSEL

INTA
INTB

IOW#

IOR#

Reset

TXRDYA#

TXRDYB#

CTS#A/B, RI#A/B,
CD#A/B, DSR#A/B

RXA (or RXIRA)

Modem Control Logic

DTR#A/B, RTS#A/B

TXB (or TXIRB)

RXB (or RXIRB)

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

PIN DESCRIPTIONS

Pin Description

AME

44-PLCC

YPE

ESCRIPTION

DATA BUS INTERFACE

Address data lines [2:0]. These 3 address lines select one of the internal registers in
UART channel A/B during a data bus transaction.

I/O

Data bus lines [7:0] (bidirectional).

IOR#

Input/Output Read Strobe (active low). The falling edge instigates an internal read
cycle and retrieves the data byte from an internal register pointed to by the address
lines [A2:A0]. The data byte is placed on the data bus to allow the host processor to
read it on the rising edge.

IOW#

Input/Output Write Strobe (active low). The falling edge instigates an internal write
cycle and the rising edge transfers the data byte on the data bus to an internal regis-
ter pointed by the address lines.

CS#

UART chip select (active low). This function selects channel A or B in accordance
with the logical state of the CHSEL pin. This allows data to be transferred between
the user CPU and the 2752.

CHSEL

Channel Select - UART channel A or B is selected by the logical state of this pin when
the CS# pin is a logic 0. A logic 0 on the CHSEL selects the UART channel B while a
logic 1 selects UART channel A. Normally, CHSEL could just be an address line from
the user CPU such as A4. Bit-0 of the Alternate Function Register (AFR) can tempo-
rarily override CHSEL function, allowing the user to write to both channel register
simultaneously with one write cycle when CS# is low. It is especially useful during the
initialization routine.

INTA

UART channel A Interrupt output (active high). A logic high indicates channel A is
requesting for service. For more details, see

Figures

INTB

UART channel B Interrupt output (active high). A logic high indicates channel B is
requesting for service. For more details, see

Figures

TXRDYA#

UART channel A Transmitter Ready (active low). The output provides the TX
FIFO/THR status for transmit channel A. See

Table 2 on page 8

TXRDYB#

UART channel B Transmitter Ready (active low). The output provides the TX FIFO/
THR status for transmit channel B.

See

Table 2 on page 8

MODEM OR SERIAL I/O INTERFACE

TXA

UART channel A Transmit Data or infrared encoder data. Standard transmit and
receive interface is enabled when MCR[6] = 0. In this mode, the TX signal will be
HIGH during reset or idle (no data). Infrared IrDA transmit and receive interface is
enabled when MCR[6] = 1. In the Infrared mode, the inactive state (no data) for the
Infrared encoder/decoder interface is LOW. If it is not used, leave it unconnected.

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

RXA

UART channel A Receive Data or infrared receive data. Normal receive data input
must idle HIGH. The infrared receiver pulses typically idles LOW but can be inverted
by software control prior going in to the decoder, see MCR[6] and FCTR[2]. If this pin
is not used, tie it to VCC or pull it high via a 100k ohm resistor.

RTSA#

UART channel A Request-to-Send (active low) or general purpose output. This output
must be asserted prior to using auto RTS flow control, see EFR[6], MCR[1],
FCTR[1:0], EMSR[5:4] and IER[6]. For auto RS485 half-duplex direction control, see
FCTR[3] and EMSR[3].

CTSA#

UART channel A Clear-to-Send (active low) or general purpose input. It can be used
for auto CTS flow control, see EFR[7], and IER[7]. This input should be connected to
VCC when not used.

DTRA#

UART channel A Data-Terminal-Ready (active low) or general purpose output. If this
pin is not used, leave it unconnected.

DSRA#

UART channel A Data-Set-Ready (active low) or general purpose input. This input
should be connected to VCC when not used. This input has no effect on the UART.

CDA#

UART channel A Carrier-Detect (active low) or general purpose input. This input
should be connected to VCC when not used. This input has no effect on the UART.

RIA#

UART channel A Ring-Indicator (active low) or general purpose input. This input
should be connected to VCC when not used. This input has no effect on the UART.

MFA#

Multi-Function Output Channel A. This output pin can function as the OP2A#, BAUD-
OUTA#, or RXRDYA# pin. One of these output signal functions can be selected by
the user programmable bits 1-2 of the Alternate Function Register (AFR). These sig-
nal functions are described as follows:

1) OP2A# - When OP2A# (active low) is selected, the MF# pin is LOW when MCR bit-
3 is set to a logic 1 (see MCR bit-3). MCR bit-3 defaults to a logic 1 condition after a
reset or power-up.

2) BAUDOUTA# - When BAUDOUTA# function is selected, the 16X Baud rate clock
output is available at this pin.

3) RXRDYA# - RXRDYA# (active low) is intended for monitoring DMA data transfers.
See

Table 2 on page 8

for more details.

TXB

UART channel B Transmit Data or infrared encoder data. Standard transmit and
receive interface is enabled when MCR[6] = 0. In this mode, the TX signal will be
HIGH during reset or idle (no data). Infrared IrDA transmit and receive interface is
enabled when MCR[6] = 1. In the Infrared mode, the inactive state (no data) for the
Infrared encoder/decoder interface is LOW. If it is not used, leave it unconnected.

RXB

UART channel B Receive Data or infrared receive data. Normal receive data input
must idle HIGH. The infrared receiver pulses typically idles LOW but can be inverted
by software control prior going in to the decoder, see MCR[6] and FCTR[2]. If this pin
is not used, tie it to VCC or pull it high via a 100k ohm resistor.

RTSB#

UART channel B Request-to-Send (active low) or general purpose output. This port
must be asserted prior to using auto RTS flow control, see EFR[6], MCR[1],
FCTR[1:0], EMSR[5:4] and IER[6]. For auto RS485 half-duplex direction control, see
FCTR[3] and EMSR[3].

Pin Description

AME

44-PLCC

YPE

ESCRIPTION

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

Pin type: I=Input, O=Output, I/O= Input/output, OD=Output Open Drain.

CTSB#

UART channel B Clear-to-Send (active low) or general purpose input. It can be used
for auto CTS flow control, see EFR[7], and IER[7]. This input should be connected to
VCC when not used.

DTRB#

UART channel B Data-Terminal-Ready (active low) or general purpose output. If this
pin is not used, leave it unconnected.

DSRB#

UART channel B Data-Set-Ready (active low) or general purpose input. This input
should be connected to VCC when not used. This input has no effect on the UART.

CDB#

UART channel B Carrier-Detect (active low) or general purpose input. This input
should be connected to VCC when not used. This input has no effect on the UART.

RIB#

UART channel B Ring-Indicator (active low) or general purpose input. This input
should be connected to VCC when not used. This input has no effect on the UART.

MFB#

Multi-Function Output Channel B. This output pin can function as the OP2B#, BAUD-
OUTB#, or RXRDYB# pin. One of these output signal functions can be selected by
the user programmable bits 1-2 of the Alternate Function Register (AFR). These sig-
nal functions are described as follows:

1) OP2B# - When OP2B# (active low) is selected, the MF# pin is LOW when MCR bit-
3 is set HIGH (see MCR bit-3). MCR bit-3 defaults to a logic 1 condition after a reset
or power-up.

2) BAUDOUTB# - When BAUDOUTB# function is selected, the 16X Baud rate clock
output is available at this pin.

3) RXRDYB# - RXRDYB# (active low) is intended for monitoring DMA data transfers.
See

Table 2 on page 8

for more details.

ANCILLARY SIGNALS

XTAL1

Crystal or external clock input. Caution: this input is not 5V tolerant.

XTAL2

Crystal or buffered clock output.

RESET

Reset (active high) - A longer than 40 ns HIGH pulse on this pin will reset the internal
registers and all outputs. The UART transmitter output will be held HIGH, the receiver
input will be ignored and outputs are reset during reset period (see External Reset
Conditions).

VCC

44, 33

Pwr

2.25 to 5.5V power supply. All input pins, except XTAL1, are 5V tolerant.

GND

22, 12

Pwr

Power supply common, ground.

Pin Description

AME

44-PLCC

YPE

ESCRIPTION

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

1.0

PRODUCT DESCRIPTION

The XR16L2752 (2752) integrates the functions of 2 enhanced 16C550 Universal Asynchronous Receiver and
Transmitter (UART). Each UART is independently controlled having its own set of device configuration
registers. The configuration registers set is 16550 UART compatible for control, status and data transfer.
Additionally, each UART channel has 64-bytes of transmit and receive FIFOs, automatic RTS/CTS hardware
flow control with hysteresis control, automatic Xon/Xoff and special character software flow control,
programmable transmit and receive FIFO trigger levels, FIFO level counters, infrared encoder and decoder
(IrDA ver 1.0), programmable baud rate generator with a prescaler of divide by 1 or 4, and data rate up to 6.25
Mbps with 8X sampling clock rate or 3.125 Mbps in the 16X rate. The XR16L2752 is a 2.25 to 5.5V device with
5 volt tolerant inputs. The 2752 is fabricated with an advanced CMOS process.

Enhanced Features

The 2752 DUART provides a solution that supports 64 bytes of transmit and receive FIFO memory, instead of
128 bytes provided in the XR16C2852 and 16 bytes in the ST16C2552. The 2752 is designed to work with low
supply voltage and high performance data communication systems, that require fast data processing time.
Increased performance is realized in the 2752 by the larger transmit and receive FIFOs, FIFO trigger level
control, FIFO level counters and automatic flow control mechanism. This allows the external processor to
handle more networking tasks within a given time. For example, the ST16C2552 with a 16 byte FIFO, unloads
16 bytes of receive data in 1.53 ms (This example uses a character length of 11 bits, including start/stop bits at
115.2 Kbps). This means the external CPU will have to service the receive FIFO at 1.53 ms intervals. However
with the 64 byte FIFO in the 2752, the data buffer will not require unloading/loading for 6.1 ms. This increases
the service interval giving the external CPU additional time for other applications and reducing the overall
UART interrupt servicing time. In addition, the programmable FIFO level trigger interrupt and automatic
hardware/software flow control is uniquely provided for maximum data throughput performance especially
when operating in a multi-channel system. The combination of the above greatly reduces the CPU's bandwidth
requirement, increases performance, and reduces power consumption.

The 2752 supports a half-duplex output direction control signaling pin, RTS# A/B, to enable and disable the
external RS-485 transceiver operation. It automatically switches the logic state of the output pin to the receive
state after the last stop-bit of the last character has been shifted out of the transmitter. After receiving, the logic
state of the output pin switches back to the transmit state when a data byte is loaded in the transmitter. The
auto RS-485 direction control pin is not activated after reset. To activate the direction control function, user has
to set FCTR Bit-3 to "1". This pin is normally high for receive state, low for transmit state.

Data Rate

The 2752 is capable of operation up to 3.125 Mbps at 5V with 16X internal sampling clock rate, and 6.25 Mbps
at 5V with 8X sampling clock rate. The device can operate with an external 24 MHz crystal on pins XTAL1 and
XTAL2, or external clock source of up to 50 MHz on XTAL1 pin. With a typical crystal of 14.7456 MHz and
through a software option, the user can set the prescaler bit for data rates of up to 1.84 Mbps.

The rich feature set of the 2752 is available through the internal registers. Automatic hardware/software flow
control, selectable transmit and receive FIFO trigger levels, selectable TX and RX baud rates, infrared
encoder/decoder interface, modem interface controls, and a sleep mode are all standard features.

Following a power on reset or an external reset, the 2752 is software compatible with previous generation of
UARTs 16C2552 and 16C2852.

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

2.0

FUNCTIONAL DESCRIPTIONS

2.1

CPU Interface

The CPU interface is 8 data bits wide with 3 address lines and control signals to execute data bus read and
write transactions. The 2752 data interface supports the Intel compatible types of CPUs and it is compatible to
the industry standard 16C550 UART. No clock (oscillator nor external clock) is required to operate a data bus
transaction. Each bus cycle is asynchronous using CS#, IOR# and IOW# signals. Both UART channels share
the same data bus for host operations. The data bus interconnections are shown in

Figure 3

2.2

5-Volt Tolerant Inputs

The 2752 can accept up to 5V inputs even when operating at 3.3V or 2.5V. But note that if the 2752 is
operating at 2.5V, its V

may not be high enough to meet the requirements of the V

of a CPU or a serial

transceiver that is operating at 5V. Caution: XTAL1 is not 5 volt tolerant.

2.3

Device Reset

The RESET input resets the internal registers and the serial interface outputs in both channels to their default
state (see

Table 16 on page 38

). An active high pulse of longer than 40 ns duration will be required to activate

the reset function in the device.

2.4

Device Identification and Revision

The XR16L2752 provides a Device Identification code and a Device Revision code to distinguish the part from
other devices and revisions. To read the identification code from the part, it is required to set the baud rate
generator registers DLL and DLM both to 0x00. Now reading the content of the DLM will provide 0x0A for the
XR16L2752 and reading the content of DLL will provide the revision of the part; for example, a reading of 0x01
means revision A.

2.5

Channel A and B Selection

The UART provides the user with the capability to bi-directionally transfer information between an external
CPU and an external serial communication device. A logic 0 on chip select pin (CS#) allows the user to select
the UART and then using the channel select (CHSEL) pin, the user can select channel A or B to configure,
send transmit data and/or unload receive data to/from the UART. Individual channel select functions are shown
in

Table 1

IGURE

3. XR16L2750 D

ATA

NTERCONNECTIONS

V C C

(O P 2 A # )

D S R A #

C T S A #

R T S A #

D T R A #

R X A

T X A

R IA #

C D A #

(O P 2 B # )

D S R B #

C T S B #

R T S B #

D T R B #

R X B

T X B

R IB #

C D B #

G N D

A 0
A 1
A 2

U A R T _ C S #

U A R T _ C H S E L

IO R #

IO W #

D 0
D 1
D 2
D 3
D 4
D 5
D 6
D 7

A 0
A 1

A 2

C S #

C H S E L

D 0
D 1
D 2
D 3
D 4
D 5
D 6
D 7

IO R #

IO W #

U A R T

C h a n n e l A

U A R T

C h a n n e l B

U A R T _ IN T B

U A R T _ IN T A

IN T B

IN T A

(R X R D Y A # )

T X R D Y A #

(R X R D Y A # )

T X R D Y A #

(R X R D Y B # )

T X R D Y B #

(R X R D Y B # )

T X R D Y B #

U A R T _ R E S E T

R E S E T

S e ria l In te r fa c e o f

R S -2 3 2 , R S - 4 8 5

S e ria l In te r fa c e o f

R S -2 3 2 , R S - 4 8 5

2 7 5 0 in t

(B A U D O U T B # )

(B A U D O U T A # )

P in s in p a re n th e s e s b e c o m e a v a ila b le th r o u g h th e M F # p in . M F # A /B b e c o m e s R X R D Y # A /B w h e n A F R [2 :1 ] = '1 0 '. M F # A /B b e c o m e s O P 2 # A /B
w h e n A F R [2 :1 ] = '0 0 '. M F # A /B b e c o m e s B A U D O U T # A /B w h e n A F R [1 :0 ] = '0 1 '.

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

2.6

Channel A and B Internal Registers

Each UART channel in the 2752 has a set of enhanced registers for control, monitoring and data loading and
unloading. The configuration register set is compatible to those already available in the standard single
16C550 and dual ST16C2550. These registers function as data holding registers (THR/RHR), interrupt status
and control registers (ISR/IER), a FIFO control register (FCR), receive line status and control registers (LSR/
LCR), modem status and control registers (MSR/MCR), programmable data rate (clock) divisor registers (DLL/
DLM), and a user accessible Scratchpad Register (SPR).

Beyond the general 16C2550 features and capabilities, the 2752 offers enhanced feature registers (AFR,
EMSR, FLVL, EFR, Xon/Xoff 1, Xon/Xoff 2, FCTR, TRG, FC) that provide automatic RTS and CTS hardware
flow control, Xon/Xoff software flow control, automatic RS-485 half-duplex direction output enable/disable,
FIFO trigger level control, FIFO level counters, and simultaneous writes to both channels. All the register
functions are discussed in full detail later in

"Section 3.0, UART INTERNAL REGISTERS" on page 20

2.7

Simultaneous Write to Channel A and B

During a write mode cycle, the setting of Alternate Function Register (AFR) bit-0 to a logic 1 will override the
CHSEL selection and allows a simultaneous write to both UART channel sections. This functional capability
allow the registers in both UART channels to be modified concurrently, saving individual channel initialization
time. Caution should be considered, however, when using this capability. Any in-process serial data transfer
may be disrupted by changing an active channel's mode.

2.8

DMA Mode

The device does not support direct memory access. The DMA Mode (a legacy term) in this document doesn't
mean "direct memory access" but refers to data block transfer operation. The DMA mode affects the state of
the RXRDY# A/B (MF# A/B becomes RXRDY# A/B output when AFR[2:1] = `10') and TXRDY# A/B output
pins. The transmit and receive FIFO trigger levels provide additional flexibility to the user for block mode
operation. The LSR bits 5-6 provide an indication when the transmitter is empty or has an empty location(s) for
more data. The user can optionally operate the transmit and receive FIFO in the DMA mode (FCR bit-3=1).
When the transmit and receive FIFO are enabled and the DMA mode is disabled (FCR bit-3 = 0), the 2752 is
placed in single-character mode for data transmit or receive operation. When DMA mode is enabled (FCR bit-
3 = 1), the user takes advantage of block mode operation by loading or unloading the FIFO in a block
sequence determined by the programmed trigger level. In this mode, the 2752 sets the TXRDY# pin when the
transmit FIFO becomes full, and sets the RXRDY# pin when the receive FIFO becomes empty. The following
table shows their behavior. Also see

Figures 18

through

ABLE

1: C

HANNEL

AND

B S

ELECT

CS#

CHSEL

UNCTION

UART de-selected

Channel A selected

Channel B selected

ABLE

2: TXRDY#

AND

RXRDY# O

UTPUTS

FIFO

AND

DMA M

ODE

INS

FCR

BIT

-0=0

(FIFO D

ISABLED

)

FCR B

-0=1 (FIFO E

NABLED

)

FCR Bit-3 = 0

(DMA Mode Disabled)

FCR Bit-3 = 1

(DMA Mode Enabled)

RXRDY# A/B LOW = 1 byte.

HIGH = no data.

LOW = at least 1 byte in FIFO.

HIGH = FIFO empty.

HIGH to LOW transition when FIFO reaches the
trigger level, or time-out occurs.

LOW to HIGH transition when FIFO empties.

TXRDY# A/B LOW = THR empty.

HIGH = byte in THR.

LOW = FIFO empty.

HIGH = at least 1 byte in FIFO.

LOW = FIFO has at least 1 empty location.

HIGH = FIFO is full.

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

2.9

INTA and INTB Outputs

The INTA and INTB interrupt output changes according to the operating mode and enhanced features setup.

Table 3

and 4

summarize the operating behavior for the transmitter and receiver. Also see

Figures 18

through

2.10

Crystal Oscillator or External Clock Input

The 2752 includes an on-chip oscillator (XTAL1 and XTAL2) to produce a clock for both UART sections in the
device. The CPU data bus does not require this clock for bus operation. The crystal oscillator provides a
system clock to the Baud Rate Generators (BRG) section found in each of the UART. XTAL1 is the input to the
oscillator or external clock buffer input with XTAL2 pin being the output. For programming details, see
"Programmable Baud Rate Generator."

ABLE

3: INTA

AND

INTB P

INS

PERATION

FOR

RANSMITTER

Auto RS485

Mode

FCR B

-0 = 0

(FIFO D

ISABLED

)

FCR B

-0 = 1 (FIFO E

NABLED

)

INTA/B Pin

LOW = a byte in THR

HIGH = THR empty

LOW = FIFO above trigger level

HIGH = FIFO below trigger level or FIFO empty

INTA/B Pin

YES

LOW = a byte in THR

HIGH = transmitter empty

LOW = FIFO above trigger level

HIGH = FIFO below trigger level or transmitter empty

ABLE

4: INTA

AND

INTB P

PERATION

ECEIVER

FCR B

-0 = 0

(FIFO D

ISABLED

)

FCR B

-0 = 1

(FIFO E

NABLED

)

INTA/B Pin

LOW = no data

HIGH = 1 byte

LOW = FIFO below trigger level

HIGH = FIFO above trigger level

IGURE

4. T

YPICAL

OSCILLATOR

CONNECTIONS

22-47 pF

1.8432 MHz

24 MHz

0-120

(Optional)

500 K

- 1 M

XTAL1

XTAL2

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

The on-chip oscillator is designed to use an industry standard microprocessor crystal (parallel resonant,
fundamental frequency with 10-22 pF capacitance load, ESR of 20-120 ohms and 100ppm frequency
tolerance) connected externally between the XTAL1 and XTAL2 pins (see

Figure 4

). The programmable Baud

Rate Generator is capable of operating with a crystal oscillator frequency of up to 24 MHz. However, with an
external clock input on XTAL1 pin and a 2K ohms pull-up resistor on XTAL2 pin (as shown in

Figure 5

) it can

extend its operation up to 50 MHz (6.25 Mbps serial data rate) and 5V with an 8X sampling rate.

For further reading on the oscillator circuit please see the Application Note DAN108 on the EXAR web site at

http://www.exar.com.

2.11

Programmable Baud Rate Generator

Each UART has its own Baud Rate Generator (BRG) with a prescaler. The prescaler is controlled by a
software bit in the MCR register. The MCR register bit-7 sets the prescaler to divide the input crystal or external
clock by 1 or 4. The clock output of the prescaler goes to the BRG. The BRG further divides this clock by a

programmable divisor between 1 and (2

-1) to obtain a 16X sampling rate clock of the serial data rate. The

sampling rate clock is used by the transmitter for data bit shifting and

receiver for data sampling. The BRG

divisor defaults to the maximum baud rate (DLL = 0x01 and DLM = 0x00) upon power up.

Programming the Baud Rate Generator Registers DLM and DLL provides the capability of selecting the
operating data rate.

Table 5

shows the standard data rates available with a 14.7456 MHz crystal or external

clock at 16X sampling rate clock rate. A 16X sampling clock is typically used. However, user can select the 8X
sampling clock rate mode (EMSR bit-7=0) to double the operating data rate. When using a non-standard data
rate crystal or external clock, the divisor value can be calculated for DLL/DLM with the following equation.

IGURE

5. E

XTERNAL

LOCK

ONNECTION

FOR

XTENDED

ATA

ATE

IGURE

6. B

AUD

ATE

ENERATOR

AND

RESCALER

XTAL1

XTAL2

VCC

External Clock

vcc

gnd

X T A L 1

X T A L 2

C ry s ta l

O s c /

B u ffe r

M C R B it-7 = 0

(d e fa u lt)

M C R B it-7 = 1

D L L a n d D L M

R e g is te rs

P re s c a le r

D iv id e b y 1

P re s c a le r

D iv id e b y 4

1 6 X

S a m p lin g

R a te C lo c k to

T ra n s m itte r

B a u d R a te

G e n e ra to r

L o g ic

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

2.12

Transmitter

The transmitter section comprises of an 8-bit Transmit Shift Register (TSR) and 64 bytes of FIFO which
includes a byte-wide Transmit Holding Register (THR). TSR shifts out every data bit with the 16X internal
clock. A bit time is 16 clock periods (see EMSR bit-7). The transmitter sends the start-bit followed by the
number of data bits, inserts the proper parity-bit if enabled, and adds the stop-bit(s). The status of the FIFO
and TSR are reported in the Line Status Register (LSR bit-5 and bit-6).

2.12.1

Transmit Holding Register (THR) - Write Only

The transmit holding register is an 8-bit register providing a data interface to the host processor. The host
writes transmit data byte to the THR to be converted into a serial data stream including start-bit, data bits,
parity-bit and stop-bit(s). The least-significant-bit (Bit-0) becomes first data bit to go out. The THR is the input
register to the transmit FIFO of 64 bytes when FIFO operation is enabled by FCR bit-0. Every time a write
operation is made to the THR, the FIFO data pointer is automatically bumped to the next sequential data
location.

2.12.2

Transmitter Operation in non-FIFO Mode

The host loads transmit data to THR one character at a time. The THR empty flag (LSR bit-5) is set when the
data byte is transferred to TSR. THR flag can generate a transmit empty interrupt (ISR bit-1) when it is enabled
by IER bit-1. The TSR flag (LSR bit-6) is set when TSR becomes completely empty.

divisor (decimal) = (XTAL1 clock frequency / prescaler) / (serial data rate x 16), with 16XMode [EMSR bit-7] = 1

divisor (decimal) = (XTAL1 clock frequency / prescaler) / (serial data rate x 8), with 16XMode [EMSR bit-7] = 0

ABLE

5: T

YPICAL

DATA

RATES

WITH

14.7456 MH

CRYSTAL

EXTERNAL

CLOCK

UTPUT

Data Rate

MCR Bit-7=1

UTPUT

Data Rate

MCR Bit-7=0

EFAULT

)

IVISOR

FOR

16x

Clock (Decimal)

IVISOR

FOR

16x

Clock (HEX)

DLM

ROGRAM

ALUE

(HEX)

DLL

ROGRAM

ALUE

(HEX)

ATA

ATE

RROR

(%)

100

400

2304

900

600

2400

384

180

1200

4800

192

2400

9600

4800

19.2k

9600

38.4k

19.2k 76.8k

38.4k

153.6k

57.6k

230.4k

115.2k 460.8k

230.4k

921.6k

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

2.12.3

Transmitter Operation in FIFO Mode

The host may fill the transmit FIFO with up to 64 bytes of transmit data. The THR empty flag (LSR bit-5) is set
whenever the FIFO is empty. The THR empty flag can generate a transmit empty interrupt (ISR bit-1) when the
amount of data in the FIFO falls below its programmed trigger level. The transmit empty interrupt is enabled by
IER bit-1. The TSR flag (LSR bit-6) is set when TSR/FIFO becomes empty.

2.13

Receiver

The receiver section contains an 8-bit Receive Shift Register (RSR) and 64 bytes of FIFO which includes a
byte-wide Receive Holding Register (RHR). The RSR uses the 16X for timing. It verifies and validates every bit
on the incoming character in the middle of each data bit. On the falling edge of a start or false start bit, an
internal receiver counter starts counting at the 16X. After 8 clocks the start bit period should be at the center of
the start bit. At this time the start bit is sampled and if it is still a logic 0 it is validated. Evaluating the start bit in
this manner prevents the receiver from assembling a false character. The rest of the data bits and stop bits are
sampled and validated in this same manner to prevent false framing. If there were any error(s), they are
reported in the LSR register bits 2-4. Upon unloading the receive data byte from RHR, the receive FIFO pointer
is bumped and the error tags are immediately updated to reflect the status of the data byte in RHR register.
RHR can generate a receive data ready interrupt upon receiving a character or delay until it reaches the FIFO
trigger level. Furthermore, data delivery to the host is guaranteed by a receive data ready time-out interrupt

IGURE

7. T

RANSMITTER

PERATION

NON

-FIFO M

ODE

IGURE

8. T

RANSMITTER

PERATION

FIFO

AND

LOW

ONTROL

ODE

Transmit

Holding

(THR)

Transmit Shift Register (TSR)

Data

Byte

L
S
B

M
S
B

THR Interrupt (ISR bit-1)

Enabled by IER bit-1

TXNOFIFO1

16X or 8X Clock

(EMSR bit-7)

Transm it Data Shift Register

(TSR)

Transm it

Data Byte

THR Interrupt (ISR bit-1) falls
below the program m ed Trigger
Level and then when becom es
em pty. FIFO is Enabled by FCR
bit-0=1

Transm it

FIFO

16X or 8X Clock

(EM SR bit-7 = 1)

Auto CTS Flow Control (CTS# pin)

Auto Software Flow Control

Flow Control Characters

(Xoff1/2 and Xon1/2 Reg.

T XF IF O 1

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

when data is not received for 4 word lengths as defined by LCR[1,0] plus 12 bits time. This is equivalent to 3.7-
4.6 character times. The RHR interrupt is enabled by IER bit-0.

2.13.1

Receive Holding Register (RHR) - Read-Only

The Receive Holding Register is an 8-bit register that holds a receive data byte from the Receive Shift
Register. It provides the receive data interface to the host processor. The RHR register is part of the receive
FIFO of 64 bytes by 11-bits wide, the 3 extra bits are for the 3 error tags to be reported in LSR register. When
the FIFO is enabled by FCR bit-0, the RHR contains the first data character received by the FIFO. After the
RHR is read, the next character byte is loaded into the RHR and the errors associated with the current data
byte are immediately updated in the LSR bits 2-4.

OTE

Table-B selected as Trigger Table for

Figure 10

(

Table 10 on page 27

IGURE

9. R

ECEIVER

PERATION

NON

-FIFO M

ODE

IGURE

10. R

ECEIVER

PERATION

FIFO

AND

UTO

RTS F

LOW

ONTROL

ODE

Receive Data Shift

Receive

Data Byte

and Errors

RHR Interrupt (ISR bit-2)

Receive Data

Holding Register

(RHR)

RXFIFO1

16X or 8X Clock

(EMSR bit-7)

Receive Data Characters

Data Bit

Validation

Error

Tags in

LSR bits

4:2

Receive Data Shift

RXFIFO1

16X or 8X Clock

(EMSR bit-7)

rro

r
T

-
s

)

rro

r
T

t
s

:
2

64 bytes by 11-bit

wide
FIFO

Receive Data Characters

FIFO Trigger=16

Example

- RX FIFO trigger level selected at 16

bytes

(See Note Below)

Data fills to 24

Data falls to 8

Data Bit

Validation

Receive

Data FIFO

Receive

Data

Receive Data
Byte and Errors

RHR Interrupt (ISR bit-2) programmed for
desired FIFO trigger level.
FIFO is Enabled by FCR bit-0=1

RTS# de-asserts when data fills above the flow
control trigger level to suspend remote transmitter.
Enable by EFR bit-6=1, MCR bit-2.

RTS# re-asserts when data falls below the flow
control trigger level to restart remote transmitter.
Enable by EFR bit-6=1, MCR bit-2.

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

2.14

Auto RTS (Hardware) Flow Control

Automatic RTS hardware flow control is used to prevent data overrun to the local receiver FIFO. The RTS#
output is used to request remote unit to suspend/resume data transmission. The auto RTS flow control
features is enabled to fit specific application requirement (see

Figure 11

Enable auto RTS flow control using EFR bit-6.

The auto RTS function must be started by asserting RTS# output pin (MCR bit-1 to logic 1 after it is enabled).

If using the Auto RTS interrupt:

Enable RTS interrupt through IER bit-6 (after setting EFR bit-4). The UART issues an interrupt when the
RTS# pin makes a transition from low to high: ISR bit-5 will be set to logic 1.

2.15

Auto RTS Hysteresis

The 2752 has a new feature that provides flow control trigger hysteresis while maintaining compatibility with
the XR16C850, ST16C650A and ST16C550 family of UARTs. With the Auto RTS function enabled, an interrupt
is generated when the receive FIFO reaches the programmed RX trigger level. The RTS# pin will not be forced
HIGH (RTS off), until the receive FIFO reaches the upper limit of the hysteresis level. The RTS# pin will return
LOW after the RX FIFO is unloaded to the lower limit of the hysteresis level. Under the above described
conditions, the 2752 will continue to accept data until the receive FIFO gets full. The Auto RTS function is
initiated when the RTS# output pin is asserted LOW (RTS On).

Table 13

shows the complete details for the

Auto RTS# Hysteresis levels. Please note that this table is for programmable trigger levels only (Table D). The
hysteresis values for Tables A-C are the next higher and next lower trigger levels in Tables A-C.

2.16

Auto CTS Flow Control

Automatic CTS flow control is used to prevent data overrun to the remote receiver FIFO. The CTS# input is
monitored to suspend/restart the local transmitter. The auto CTS flow control feature is selected to fit specific
application requirement (see

Figure 11

Enable auto CTS flow control using EFR bit-7.

If using the Auto CTS interrupt:

Enable CTS interrupt through IER bit-7 (after setting EFR bit-4). The UART issues an interrupt when the
CTS# pin is de-asserted (HIGH): ISR bit-5 will be set to 1, and UART will suspend transmission as soon as
the stop bit of the character in process is shifted out. Transmission is resumed after the CTS# input is re-
asserted (LOW), indicating more data may be sent.

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

IGURE

11. A

UTO

RTS

AND

CTS F

LOW

ONTROL

PERATION

The local UART (UARTA) starts data transfer by asserting RTSA# (1). RTSA# is normally connected to CTSB# (2) of

remote UART (UARTB). CTSB# allows its transmitter to send data (3). TXB data arrives and fills UARTA receive FIFO
(4). When RXA data fills up to its receive FIFO trigger level, UARTA activates its RXA data ready interrupt (5) and con-
tinues to receive and put data into its FIFO. If interrupt service latency is long and data is not being unloaded, UARTA
monitors its receive data fill level to match the upper threshold of RTS delay and de-assert RTSA# (6). CTSB# follows
(7) and request UARTB transmitter to suspend data transfer. UARTB stops or finishes sending the data bits in its trans-
mit shift register (8). When receive FIFO data in UARTA is unloaded to match the lower threshold of RTS delay (9),
UARTA re-asserts RTSA# (10), CTSB# recognizes the change (11) and restarts its transmitter and data flow again until
next receive FIFO trigger (12). This same event applies to the reverse direction when UARTA sends data to UARTB
with RTSB# and CTSA# controlling the data flow.

RTSA#

CTSB#

RXA

TXB

Transmitter

Receiver FIFO

Trigger Reached

Auto RTS

Trigger Level

Auto CTS

Monitor

RTSA#

TXB

RXA FIFO

CTSB#

Remote UART

UARTB

Local UART

UARTA

OFF

Suspend

Restart

RTS High

Threshold

Data Starts

OFF

Assert RTS# to Begin

Transmission

Receive

Data

RTS Low

Threshold

Receiver FIFO

Trigger Reached

Auto RTS

Trigger Level

Transmitter

Auto CTS

Monitor

RTSB#

CTSA#

RXB

TXA

INTA

(RXA FIFO

Interrupt)

RX FIFO

Trigger Level

RX FIFO

Trigger Level

RTSCTS1

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

2.17

Auto Xon/Xoff (Software) Flow Control

When software flow control is enabled (

See Table 15

), the 2752 compares one or two sequential receive data

characters with the programmed Xon or Xoff-1,2 character value(s). If receive character(s) (RX) match the
programmed values, the 2752 will halt transmission (TX) as soon as the current character has completed
transmission. When a match occurs, the Xoff (if enabled via IER bit-5) flag will be set and the interrupt output
pin will be activated. Following a suspension due to a match of the Xoff character, the 2752 will monitor the
receive data stream for a match to the Xon-1,2 character. If a match is found, the 2752 will resume operation
and clear the flags (ISR bit-4).

Reset initially sets the contents of the Xon/Xoff 8-bit flow control registers to a logic 0. Following reset the user
can write any Xon/Xoff value desired for software flow control. Different conditions can be set to detect Xon/
Xoff characters (

See Table 15

) and suspend/resume transmissions. When double 8-bit Xon/Xoff characters are

selected, the 2752 compares two consecutive receive characters with two software flow control 8-bit values
(Xon1, Xon2, Xoff1, Xoff2) and controls TX transmissions accordingly. Under the above described flow control
mechanisms, flow control characters are not placed (stacked) in the user accessible RX data buffer or FIFO.

In the event that the receive buffer is overfilling and flow control needs to be executed, the 2752 automatically
sends an Xoff message (when enabled) via the serial TX output to the remote modem. The 2752 sends the
Xoff-1,2 characters two-character-times (= time taken to send two characters at the programmed baud rate)
after the receive FIFO crosses the programmed trigger level (for all trigger tables A-D). To clear this condition,
the 2752 will transmit the programmed Xon-1,2 characters as soon as receive FIFO is less than one trigger
level below the programmed trigger level (for Trigger Tables A, B, and C) or when receive FIFO is less than the
trigger level minus the hysteresis value (for Trigger Table D). This hysteresis value is the same as the Auto
RTS Hysteresis value in

Table 13

Table 6

below explains this when Trigger Table-B (See

Table 10

) is selected.

After the trigger level is reached, an xoff character is sent after a short span of time (= time required to send 2

characters); for example, after 2.083ms has elapsed for 9600 baud and 10-bit word length setting.

2.18

Special Character Detect

A special character detect feature is provided to detect an 8-bit character when bit-5 is set in the Enhanced
Feature Register (EFR). When this character (Xoff2) is detected, it will be placed in the FIFO along with normal
incoming RX data.

The 2752 compares each incoming receive character with Xoff-2 data. If a match exists, the received data will
be transferred to FIFO and ISR bit-4 will be set to indicate detection of special character. Although the Internal
Register Table shows Xon, Xoff Registers with eight bits of character information, the actual number of bits is
dependent on the programmed word length. Line Control Register (LCR) bits 0-1 defines the number of
character bits, i.e., either 5 bits, 6 bits, 7 bits, or 8 bits. The word length selected by LCR bits 0-1 also
determines the number of bits that will be used for the special character comparison. Bit-0 in the Xon, Xoff
Registers corresponds with the LSB bit for the receive character.

2.19

Auto RS485 Half-duplex Control

The auto RS485 half-duplex direction control changes the behavior of the transmitter when enabled by FCTR
bit-3. By default, it de-asserts RTS# (HIGH) output following

the last stop bit of the last character that has been

transmitted. This helps in turning around the transceiver to receive the remote station's response. When the
host is ready to transmit next polling data packet again, it only has to load data bytes to the transmit FIFO. The
transmitter automatically re-asserts RTS# (LOW) output prior to sending the data. The RS485 half-duplex
direction control output can be inverted by enabling EMSR bit-3.

ABLE

6: A

UTO

OFF

OFTWARE

) F

LOW

ONTROL

RX T

RIGGER

EVEL

INT P

CTIVATION

OFF

HARACTER

(

) S

ENT

(

CHARACTERS

FIFO

)

HARACTER

(

) S

ENT

(

CHARACTERS

FIFO

)

16*

24*

28*

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

2.21

Sleep Mode with Auto Wake-Up

The 2752 supports low voltage system designs, hence, a sleep mode is included to reduce its power
consumption when the chip is not actively used.

All of these conditions must be satisfied for the 2752 to enter sleep mode:

no interrupts pending for both channels of the 2752 (ISR bit-0 = 1)

sleep mode of both channels are enabled (IER bit-4 = 1)

modem inputs are not toggling (MSR bits 0-3 = 0)

RX input pins are idling HIGH

The 2752 stops its crystal oscillator to conserve power in the sleep mode. User can check the XTAL2 pin for
no clock output as an indication that the device has entered the sleep mode.

The 2752 resumes normal operation by any of the following:

a receive data start bit transition (HIGH to LOW)

a data byte is loaded to the transmitter, THR or FIFO

a change of logic state on any of the modem or general purpose serial inputs: CTS#, DSR#, CD#, RI#

If the 2752 is awakened by any one of the above conditions, it will return to the sleep mode automatically after
all interrupting conditions have been serviced and cleared. If the 2752 is awakened by the modem inputs, a
read to the MSR is required to reset the modem inputs. In any case, the sleep mode will not be entered while
an interrupt is pending from channel A or B. The 2752 will stay in the sleep mode of operation until it is disabled
by setting IER bit-4 to a logic 0.

If the address lines, data bus lines, IOW#, IOR#, CSA#, CSB#, and modem input lines remain steady when the
2752 is in sleep mode, the maximum current will be in the microamp range as specified in the DC Electrical
Characteristics on

page 39

. If the input lines are floating or are toggling while the 2752 is in sleep mode, the

current can be up to 100 times more. If any of those signals are toggling or floating, then an external buffer
would be required to keep the address, data and control lines steady to achieve the low current. As an
alternative, please refer to the XR16L2751 with the PowerSave feature that eliminates any unnecessary
external buffer.

A word of caution: owing to the starting up delay of the crystal oscillator after waking up from sleep mode, the
first few receive characters may be lost. The number of characters lost during the restart also depends on your
operating data rate. More characters are lost when operating at higher data rate. Also, it is important to keep
RX A/B inputs idling HIGH or "marking" condition during sleep mode to avoid receiving a "break" condition
upon the restart. This may occur when the external interface transceivers (RS-232, RS-485 or another type)
are also put to sleep mode and cannot maintain the "marking" condition. To avoid this, the designer can use a
47k-100k ohm pull-up resistor on the RXA and RXB pins.

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

3.0

UART INTERNAL REGISTERS

Each of the UART channel in the 2752 has its own set of configuration registers selected by address lines A0,
A1 and A2 with CS# and CHSEL selecting the channel. The complete register set is shown in

Table 7

and

Table 8

ABLE

7: UART CHANNEL A AND B UART INTERNAL REGISTERS

DDRESSES

A2 A1 A0

EGISTER

EAD

RITE

OMMENTS

16C550 C

OMPATIBLE

EGISTERS

0 0 0

RHR - Receive Holding Register

THR - Transmit Holding Register

Read-only

Write-only

LCR[7] = 0

0 0 0

DLL - Div Latch Low Byte

Read/Write

LCR[7] = 1, LCR

0xBF

0 0 1

DLM - Div Latch High Byte

Read/Write

0 1 0

AFR - Alternate Function Register

Read/Write

0 0 0

DREV - Device Revision Code

Read-only

DLL, DLM

= 0x00,

LCR[7] = 1, LCR

0xBF

0 0 1

DVID - Device Identification Code

Read-only

0 0 1

IER - Interrupt Enable Register

Read/Write

LCR[7] = 0

0 1 0

ISR - Interrupt Status Register

FCR - FIFO Control Register

Read-only

Write-only

LCR[7] = 0

0 1 1

LCR - Line Control Register

Read/Write

1 0 0

MCR - Modem Control Register

Read/Write

LCR

0xBF

1 0 1

LSR - Line Status Register

Reserved

Read-only

Write-only

1 1 0

MSR - Modem Status Register

Reserved

Read-only

Write-only

1 1 1

SPR - Scratch Pad Register

Read/Write

LCR

0xBF, FCTR[6] = 0

1 1 1

FLVL - RX/TX FIFO Level Counter Register

Read-only

LCR

0xBF, FCTR[6] = 1

1 1 1

EMSR - Enhanced Mode Select Register

Write-only

NHANCED

EGISTERS

0 0 0

TRG -RX/TX FIFO Trigger Level Register

FC - RX/TX FIFO Level Counter Register

Write-only

Read-only

LCR = 0xBF

0 0 1

FCTR - Feature Control Register

Read/Write

0 1 0

EFR - Enhanced Function Register

Read/Write

1 0 0

Xon-1 - Xon Character 1

Read/Write

1 0 1

Xon-2 - Xon Character 2

Read/Write

1 1 0

Xoff-1 - Xoff Character 1

Read/Write

1 1 1

Xoff-2 - Xoff Character 2

Read/Write

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

ABLE

8: INTERNAL REGISTERS DESCRIPTION.

HADED

BITS

ARE

ENABLED

WHEN

EFR B

-4=1

DDRESS

A2-A0

AME

EAD

RITE

-7

-6

-5

-4

-3

-2

-1

-0

OMMENT

16C550 Compatible Registers

0 0 0

RHR

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

LCR[7] = 0

0 0 0

THR

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

0 0 1

IER

RD/WR

Modem

Stat.

Int.

Enable

RX Line

Stat.

Int.

Enable

Empty

Int

Enable

Data

Int.

Enable

CTS Int.

Enable

RTS Int.

Enable

Xoff Int.

Enable

Sleep

Mode

Enable

0 1 0

ISR

FIFOs

Enabled

FIFOs

Enabled

INT

Source

Bit-3

INT

Source

Bit-2

INT

Source

Bit-1

INT

Source

Bit-0

INT

Source

Bit-5

INT

Source

Bit-4

0 1 0

FCR

RX FIFO

Trigger

RX FIFO

Trigger

DMA

Mode

Enable

FIFO

Reset

FIFO

Reset

FIFOs

Enable

TX FIFO

Trigger

TX FIFO

Trigger

0 1 1

LCR

RD/WR

Divisor
Enable

Set TX

Break

Set Par-

ity

Even

Parity

Enable

Stop

Bits

Word

Length

Bit-1

Word

Length

Bit-0

1 0 0

MCR

RD/WR

Internal

Lopback

Enable

OP2#

Output

Control

Rsrvd

(OP1#)

RTS#

Output

Control

DTR#

Output

Control

LCR

0xBF

BRG

Pres-

caler

IR Mode

ENable

XonAny

1 0 1

LSR

RX FIFO

Global

Error

THR &

TSR

Empty

THR

Empty

Break

Fram-

ing

Error

Parity

Error

Over-

run

Error

Data

Ready

1 1 0

MSR

CD#

Input

RI#

Input

DSR#

Input

CTS#

Input

Delta

CD#

Delta

RI#

Delta

DSR#

Delta

CTS#

1 1 1

SPR

RD/WR

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

LCR

0xBF

FCTR bit-6=0

1 1 1

EMSR

16X

Sam-

pling
Rate

Mode

LSR

Error

Inter-

rupt.

Imd/Dly#

Auto

RTS

Hyst.

bit-3

Auto

RTS

Hyst.

bit-2

Auto

RS485
Output

Inver-

sion

Rsrvd

Rx/Tx

FIFO

Count

Rx/Tx

FIFO

Count

LCR

0xBF

FCTR bit-6=1

1 1 1

FLVL

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

4.0

INTERNAL REGISTER DESCRIPTIONS

4.1

Receive Holding Register (RHR) - Read- Only

See "Receiver" on page 12.

4.2

Transmit Holding Register (THR) - Write-Only

See "Transmitter" on page 11.

4.3

Interrupt Enable Register (IER) - Read/Write

The Interrupt Enable Register (IER) masks the interrupts from receive data ready, transmit empty, line status
and modem status registers. These interrupts are reported in the Interrupt Status Register (ISR).

Baud Rate Generator Divisor

0 0 0

DLL

RD/WR

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

LCR[7] = 1

LCR

0xBF

0 0 1

DLM

RD/WR

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

0 1 0

AFR

RD/WR

Rsvd

RXRDY#

Select

Baudout#

Select

Concur-

rent Write

0 0 0

DREV

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

LCR[7] = 1

LCR

0xBF

DLL=0x00

DLM=0x00

0 0 1

DVID

Enhanced Registers

0 0 0

TRG

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

LCR=0

0 0 0

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

0 0 1

FCTR

RD/WR

RX/TX

Mode

SCPAD

Swap

Trig

Table

Bit-1

Trig

Table

Bit-0

Auto

RS485

Direc-

tion

Control

RX IR

Input

Inv.

Auto
RTS
Hyst
Bit-1

Auto
RTS
Hyst
Bit-0

0 1 0

EFR

RD/WR

Auto
CTS

Enable

Auto
RTS

Enable

Special

Char

Select

Enable

IER [7:4],
ISR [5:4],

FCR[5:4],

MCR[7:5]

Soft-
ware
Flow

Cntl

Bit-3

Soft-
ware
Flow

Cntl

Bit-2

Soft-
ware
Flow

Cntl

Bit-1

Soft-
ware
Flow

Cntl

Bit-0

1 0 0

XON1

RD/WR

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

1 0 1

XON2

RD/WR

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

1 1 0

XOFF1 RD/WR

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

1 1 1

XOFF2 RD/WR

Bit-7

Bit-6

Bit-5

Bit-4

Bit-3

Bit-2

Bit-1

Bit-0

ABLE

8: INTERNAL REGISTERS DESCRIPTION.

HADED

BITS

ARE

ENABLED

WHEN

EFR B

-4=1

DDRESS

A2-A0

AME

EAD

RITE

-7

-6

-5

-4

-3

-2

-1

-0

OMMENT

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

4.3.1

IER versus Receive FIFO Interrupt Mode Operation

When the receive FIFO (FCR BIT-0 = 1) and receive interrupts (IER BIT-0 = 1) are enabled, the RHR interrupts
(see ISR bits 2 and 3) status will reflect the following:

A. The receive data available interrupts are issued to the host when the FIFO has reached the programmed

trigger level. It will be cleared when the FIFO drops below the programmed trigger level.

B. FIFO level will be reflected in the ISR register when the FIFO trigger level is reached. Both the ISR register

status bit and the interrupt will be cleared when the FIFO drops below the trigger level.

C. The receive data ready bit (LSR BIT-0) is set as soon as a character is transferred from the shift register to

the receive FIFO. It is reset when the FIFO is empty.

4.3.2

IER versus Receive/Transmit FIFO Polled Mode Operation

When FCR BIT-0 equals a logic 1 for FIFO enable; resetting IER bits 0-3 enables the XR16L2752 in the FIFO
polled mode of operation. Since the receiver and transmitter have separate bits in the LSR either or both can
be used in the polled mode by selecting respective transmit or receive control bit(s).

A. LSR BIT-0 indicates there is data in RHR

RX FIFO.

B. LSR BIT-1 indicates an overrun error has occurred and that data in the FIFO may not be valid.

C. LSR BIT 2-4 provides the type of receive data errors encountered for the data byte in RHR, if any.

D. LSR BIT-5 indicates THR is empty.

E. LSR BIT-6 indicates when both the transmit FIFO and TSR are empty.

LSR BIT-7 indicates a data error in at least one character in the RX FIFO.

IER[0]: RHR Interrupt Enable

The receive data ready interrupt will be issued when RHR has a data character in the non-FIFO mode

or when

the receive FIFO has reached the programmed trigger level in the FIFO mode.

Logic 0 = Disable the receive data ready interrupt (default).

Logic 1 = Enable the receiver data ready interrupt.

IER[1]: THR Interrupt Enable

This bit enables the Transmit Ready interrupt which is issued whenever the THR becomes empty in the non-
FIFO mode or when data in the FIFO falls below the programmed trigger level in the FIFO mode. If the THR is
empty when this bit is enabled, an interrupt will be generated.

Logic 0 = Disable Transmit Ready interrupt (default).

Logic 1 = Enable Transmit Ready interrupt.

IER[2]: Receive Line Status Interrupt Enable

If any of the LSR register bits 1, 2, 3 or 4 is a logic 1, it will generate an interrupt to inform the host controller
about the error status of the current data byte in FIFO. LSR bits 1-4 generate an interrupt immediately when
the character has been received.

Logic 0 = Disable the receiver line status interrupt (default).

Logic 1 = Enable the receiver line status interrupt.

IER[3]: Modem Status Interrupt Enable

Logic 0 = Disable the modem status register interrupt (default).

Logic 1 = Enable the modem status register interrupt.

IER[4]: Sleep Mode Enable (requires EFR bit-4 = 1)

Logic 0 = Disable Sleep Mode (default).

Logic 1 = Enable Sleep Mode. See Sleep Mode section for further details.

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

IER[5]: Xoff Interrupt Enable (requires EFR bit-4=1)

Logic 0 = Disable the software flow control, receive Xoff interrupt. (default)

Logic 1 = Enable the software flow control, receive Xoff interrupt. See Software Flow Control section for
details.

IER[6]: RTS# Output Interrupt Enable (requires EFR bit-4=1)

Logic 0 = Disable the RTS# interrupt (default).

Logic 1 = Enable the RTS# interrupt. The UART issues an interrupt when the RTS# pin makes a transition
from low to high.

IER[7]: CTS# Input Interrupt Enable (requires EFR bit-4=1)

Logic 0 = Disable the CTS# interrupt (default).

Logic 1 = Enable the CTS# interrupt. The UART issues an interrupt when CTS# pin makes a transition from
low to high.

4.4

Interrupt Status Register (ISR) - Read-Only

The UART provides multiple levels of prioritized interrupts to minimize external software interaction. The
Interrupt Status Register (ISR) provides the user with six interrupt status bits. Performing a read cycle on the
ISR will give the user the current highest pending interrupt level to be serviced, others are queued up to be
serviced next. No other interrupts are acknowledged until the pending interrupt is serviced. The Interrupt
Source Table,

Table 9

, shows the data values (bit 0-5) for the interrupt priority levels and the interrupt sources

associated with each of these interrupt levels.

4.4.1

Interrupt Generation:

LSR is by any of the LSR bits 1, 2, 3 and 4.

RXRDY is by RX trigger level.

RXRDY Time-out is by a 4-char plus 12 bits delay timer.

TXRDY is by TX trigger level or TX FIFO empty (or transmitter empty in auto RS-485 control).

MSR is by any of the MSR bits 0, 1, 2 and 3.

Receive Xoff/Special character is by detection of a Xoff or Special character.

CTS# is when its transmitter toggles the input pin (from LOW to HIGH) during auto CTS flow control.

RTS# is when its receiver toggles the output pin (from LOW to HIGH) during auto RTS flow control.

4.4.2

Interrupt Clearing:

LSR interrupt is cleared by a read to the LSR register.

RXRDY interrupt is cleared by reading data until FIFO falls below the trigger level.

RXRDY Time-out interrupt is cleared by reading RHR.

TXRDY interrupt is cleared by a read to the ISR register or writing to THR.

MSR interrupt is cleared by a read to the MSR register.

Xoff interrupt is cleared by a read to ISR or when Xon character(s) is received.

Special character interrupt is cleared by a read to ISR or after the next character is received.

RTS# and CTS# flow control interrupts are cleared by a read to the MSR register.

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

]

ISR[0]: Interrupt Status

Logic 0 = An interrupt is pending and the ISR contents may be used as a pointer to the appropriate interrupt
service routine.

Logic 1 = No interrupt pending (default condition).

ISR[3:1]: Interrupt Status

These bits indicate the source for a pending interrupt at interrupt priority levels (See Interrupt Source

Table 9

ISR[5:4]: Interrupt Status

These bits are enabled when EFR bit-4 is set to a logic 1. ISR bit-4 indicates that the receiver detected a data
match of the Xoff character(s). Note that once set to a logic 1, the ISR bit-4 will stay a logic 1 until a Xon
character is received. ISR bit-5 indicates that CTS# or RTS# has changed state.

ISR[7:6]: FIFO Enable Status

These bits are set to a logic 0 when the FIFOs are disabled. They are set to a logic 1 when the FIFOs are
enabled.

4.5

FIFO Control Register (FCR) - Write-Only

This register is used to enable the FIFOs, clear the FIFOs, set the transmit/receive FIFO trigger levels, and
select the DMA mode. The DMA, and FIFO modes are defined as follows:

FCR[0]: TX and RX FIFO Enable

Logic 0 = Disable the transmit and receive FIFO (default).

Logic 1 = Enable the transmit and receive FIFOs. This bit must be set to logic 1 when other FCR bits are
written or they will not be programmed.

FCR[1]: RX FIFO Reset

This bit is only active when FCR bit-0 is a `1'.

Logic 0 = No receive

FIFO

reset (default)

Logic 1 = Reset the receive FIFO pointers and FIFO level counter logic (the receive shift register is not
cleared or altered). This bit will return to a logic 0 after resetting the FIFO.

ABLE

9: I

NTERRUPT

OURCE

AND

RIORITY

EVEL

RIORITY

ISR R

EGISTER

TATUS

ITS

OURCE

INTERRUPT

EVEL

-5

-4

-3

-2

-1

-0

LSR (Receiver Line Status Register)

RXRDY (Receive Data Time-out)

RXRDY (Received Data Ready)

TXRDY (Transmit Ready)

MSR (Modem Status Register)

RXRDY (Received Xoff or Special character)

CTS#, RTS# change of state

None (default)

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

LCR[2]: TX and RX Stop-bit Length Select

The length of stop bit is specified by this bit in conjunction with the programmed word length.

LCR[3]: TX and RX Parity Select

Parity or no parity can be selected via this bit. The parity bit is a simple way used in communications for data
integrity check. See

Table 11

for parity selection summary below.

Logic 0 = No parity.

Logic 1 = A parity bit is generated during the transmission while the receiver checks for parity error of the
data character received.

LCR[4]: TX and RX Parity Select

If the parity bit is enabled with LCR bit-3 set to a logic 1, LCR BIT-4 selects the even or odd parity format.

Logic 0 = ODD Parity is generated by forcing an odd number of logic 1's in the transmitted character. The
receiver must be programmed to check the same format (default).

Logic 1 = EVEN Parity is generated by forcing an even number of logic 1's in the transmitted character. The
receiver must be programmed to check the same format.

LCR[5]: TX and RX Parity Select

If the parity bit is enabled, LCR BIT-5 selects the forced parity format.

LCR BIT-5 = logic 0, parity is not forced (default).

LCR BIT-5 = logic 1 and LCR BIT-4 = logic 0, parity bit is forced to a logical 1 for the transmit and receive
data.

LCR BIT-5 = logic 1 and LCR BIT-4 = logic 1, parity bit is forced to a logical 0 for the transmit and receive
data.

BIT-2

ORD

LENGTH

TOP

BIT

LENGTH

TIME

(

))

5,6,7,8

1 (default)

1-1/2

6,7,8

ABLE

11: P

ARITY

SELECTION

LCR B

-5 LCR B

-4 LCR B

-3

ARITY

SELECTION

No parity

Odd parity

Even parity

Force parity to mark,

"1"

Forced parity to

space, "0"

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

LCR[6]: Transmit Break Enable

When enabled, the Break control bit causes a break condition to be transmitted (the TX output is forced to a
"space", LOW state). This condition remains, until disabled by setting LCR bit-6 to a logic 0.

Logic 0 = No TX break condition (default).

Logic 1 = Forces the transmitter output (TX) to a "space", LOW, for alerting the remote receiver of a line
break condition.

LCR[7]: Baud Rate Divisors Enable

Baud rate generator divisor (DLL/DLM) enable.

Logic 0 = Data registers are selected (default).

Logic 1 = Divisor latch registers are selected.

4.7

Alternate Function Register (AFR) - Read/Write

This register is used to select specific modes of MF# operation and to allow both UART register sets to be
written concurrently.

AFR[0]: Concurrent Write Mode

When this bit is set, the CPU can write concurrently to the same register in both UARTs. This function is
intended to reduce the dual UART initialization time. It can be used by the CPU when both channels are
initialized to the same state. The external CPU can set or clear this bit by accessing either register set. When
this bit is set, the channel select pin still selects the channel to be accessed during read operations. The user
should ensure that LCR Bit-7 of both channels are in the same state before executing a concurrent write to the
registers at address 0, 1, or 2.

Logic 0 = No concurrent write (default).

Logic 1 = Register set A and B are written concurrently with a single external CPU I/O write operation.

AFR[2:1]: MF# Output Select

These bits select a signal function for output on the MF# A/B pins. These signal function are described as:
OP2#, BAUDOUT#, or RXRDY#. Only one signal function can be selected at a time.

AFR[7:3]: Reserved

All are initialized to logic 0.

4.8

Modem Control Register (MCR) or General Purpose Outputs Control - Read/Write

The MCR register is used for controlling the serial/modem interface signals or general purpose inputs/outputs.

MCR[0]: DTR# Output

The DTR# pin is a modem control output. If the modem interface is not used, this output may be used as a
general purpose output.

Logic 0 = Force DTR# output HIGH (default).

Logic 1 = Force DTR# output LOW.

-2

-1

MF# F

UNCTION

OP2# (default)

BAUDOUT#

RXRDY#

Reserved

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

MCR[1]: RTS# Output

The RTS# pin is a modem control output and may be used for automatic hardware flow control by enabled by
EFR bit-6. If the modem interface is not used, this output may be used as a general purpose output.

Logic 0 = Force RTS# output HIGH (default).

Logic 1 = Force RTS# output LOW.

MCR[2]: Reserved

OP1# is not available as an output pin on the 2752. But it is available for use during Internal Loopback Mode.
In the Loopback Mode, this bit is used to write the state of the modem RI# interface signal.

MCR[3]: OP2# Output / INT Output Enable

OP2# is available as an output pin on the 2752 when AFR[2:1] = `00'. In the Loopback Mode, MCR[3] is used
to write the state of the modem CD# interface signal. Also see pin descriptions for MF# pins.

Logic 0 = Forces OP2# output HIGH (default).

Logic 1 = Forces OP2# output LOW.

MCR[4]: Internal Loopback Enable

Logic 0 = Disable loopback mode (default).

Logic 1 = Enable local loopback mode, see loopback section and

Figure 13

MCR[5]: Xon-Any Enable

Logic 0 = Disable Xon-Any function (for 16C550 compatibility, default).

Logic 1 = Enable Xon-Any function. In this mode, any RX character received will resume transmit operation.
The RX character will be loaded into the RX FIFO, unless the RX character is an Xon or Xoff character and
the 2752 is programmed to use the Xon/Xoff flow control.

MCR[6]: Infrared Encoder/Decoder Enable

Logic 0 = Enable the standard modem receive and transmit input/output interface (default).

Logic 1 = Enable infrared IrDA receive and transmit inputs/outputs. The TX/RX output/input are routed to the
infrared encoder/decoder. The data input and output levels conform to the IrDA infrared interface
requirement. While in this mode, the infrared TX output will be a logic 0 during idle data conditions.

MCR[7]: Clock Prescaler Select

Logic 0 = Divide by one. The input clock from the crystal or external clock is fed directly to the Programmable
Baud Rate Generator without further modification, i.e., divide by one (default).

Logic 1 = Divide by four. The prescaler divides the input clock from the crystal or external clock by four and
feeds it to the Programmable Baud Rate Generator, hence, data rates become one forth.

4.9

Line Status Register (LSR) - Read Only

This register provides the status of data transfers between the UART and the host.

LSR[0]: Receive Data Ready Indicator

Logic 0 = No data in receive holding register or FIFO (default).

Logic 1 = Data has been received and is saved in the receive holding register or FIFO.

LSR[1]: Receiver Overrun Flag

Logic 0 = No overrun error. (default)

Logic 1 = Overrun error. A data overrun error condition occurred in the receive shift register. This happens
when additional data arrives while the FIFO is full. In this case the previous data in the receive shift register
is overwritten. Note that under this condition the data byte in the receive shift register is not transferred into
the FIFO, therefore the data in the FIFO is not corrupted by the error.

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

LSR[2]: Receive Data Parity Error Flag

Logic 0 = No parity error (default).

Logic 1 = Parity error. The receive character in RHR does not have correct parity information and is suspect.
This error is associated with the character available for reading in RHR.

LSR[3]: Receive Data Framing Error Flag

Logic 0 = No framing error (default).

Logic 1 = Framing error. The receive character did not have a valid stop bit(s). This error is associated with
the character available for reading in RHR.

LSR[4]: Receive Break Flag

Logic 0 = No break condition (default).

Logic 1 = The receiver received a break signal (RX was a logic 0 for at least one character frame time). In the
FIFO mode, only one break character is loaded into the FIFO.

LSR[5]: Transmit Holding Register Empty Flag

This bit is the Transmit Holding Register Empty indicator. The THR bit is set to a logic 1 when the last data byte
is transferred from the transmit holding register to the transmit shift register. The bit is reset to logic 0
concurrently with the data loading to the transmit holding register by the host. In the FIFO mode this bit is set
when the transmit FIFO is empty, it is cleared when the transmit FIFO contains at least 1 byte.

LSR[6]: THR and TSR Empty Flag

This bit is set to a logic 1 whenever the transmitter goes idle. It is set to logic 0 whenever either the THR or
TSR contains a data character. In the FIFO mode this bit is set to a logic 1 whenever the transmit FIFO and
transmit shift register are both empty.

LSR[7]: Receive FIFO Data Error Flag

Logic 0 = No FIFO error (default).

Logic 1 = A global indicator for the sum of all error bits in the RX FIFO. At least one parity error, framing error
or break indication is in the FIFO data. This bit clears when there is no more error(s) in any of the bytes in the
RX FIFO.

4.10

Modem Status Register (MSR) - Read Only

This register provides the current state of the modem interface input signals. Lower four bits of this register are
used to indicate the changed information. These bits are set to a logic 1 whenever a signal from the modem
changes state. These bits may be used as general purpose inputs when they are not used with modem
signals.

MSR[0]: Delta CTS# Input Flag

Logic 0 = No change on CTS# input (default).

Logic 1 = The CTS# input has changed state since the last time it was monitored. A modem status interrupt
will be generated if MSR interrupt is enabled (IER bit-3).

MSR[1]: Delta DSR# Input Flag

Logic 0 = No change on DSR# input (default).

Logic 1 = The DSR# input has changed state since the last time it was monitored. A modem status interrupt
will be generated if MSR interrupt is enabled (IER bit-3).

MSR[2]: Delta RI# Input Flag

Logic 0 = No change on RI# input (default).

Logic 1 = The RI# input has changed from a LOW to HIGH, ending of the ringing signal. A modem status
interrupt will be generated if MSR interrupt is enabled (IER bit-3).

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

MSR[3]: Delta CD# Input Flag

Logic 0 = No change on CD# input (default).

Logic 1 = Indicates that the CD# input has changed state since the last time it was monitored. A modem
status interrupt will be generated if MSR interrupt is enabled (IER bit-3).

MSR[4]: CTS Input Status

CTS# pin may function as automatic hardware flow control signal input if it is enabled and selected by Auto
CTS (EFR bit-7). Auto CTS flow control allows starting and stopping of local data transmissions based on the
modem CTS# signal. A HIGH on the CTS# pin will stop UART transmitter as soon as the current character has
finished transmission, and a LOW will resume data transmission. Normally MSR bit-4 bit is the complement of
the CTS# input. However in the loopback mode, this bit is equivalent to the RTS# bit in the MCR register. The
CTS# input may be used as a general purpose input when the modem interface is not used.

MSR[5]: DSR Input Status

Normally this bit is the complement of the DSR# input. In the loopback mode, this bit is equivalent to the DTR#
bit in the MCR register. The DSR# input may be used as a general purpose input when the modem interface is
not used.

MSR[6]: RI Input Status

Normally this bit is the complement of the RI# input. In the loopback mode this bit is equivalent to bit-2 in the
MCR register. The RI# input may be used as a general purpose input when the modem interface is not used.

MSR[7]: CD Input Status

Normally this bit is the complement of the CD# input. In the loopback mode this bit is equivalent to bit-3 in the
MCR register. The CD# input may be used as a general purpose input when the modem interface is not used.

4.11

Scratch Pad Register (SPR) - Read/Write

This is a 8-bit general purpose register for the user to store temporary data. The content of this register is
preserved during sleep mode but becomes 0xFF (default) after a reset or a power off-on cycle.

4.12

Enhanced Mode Select Register (EMSR)

This register replaces SPR (during a Write) and is accessible only when FCTR[6] = 1.

EMSR[1:0]: Receive/Transmit FIFO Count (Write-Only)

When Scratchpad Swap (FCTR[6]) is asserted, EMSR bits 1-0 controls what mode the FIFO Level Counter is
operating in.

During Alternate RX/TX FIFO Counter Mode, the first value read after EMSR bits 1-0 have been asserted will
always be the RX FIFO Counter. The second value read will correspond with the TX FIFO Counter. The next
value will be the RX FIFO Counter again, then the TX FIFO Counter and so on and so forth.

EMSR[2]: Reserved

EMSR[3]: Automatic RS485 Half-Duplex Control Output Inversion

Logic 0 = RTS# output is a logic 0 during TX and a logic 1 during RX (default, compatible with 16C2850).

Logic 1 = RTS# output is a logic 1 during TX and a logic 0 during RX.

ABLE

12: S

CRATCHPAD

WAP

ELECTION

FCTR[6] EMSR[1]

EMSR[0] Scratchpad is

Scratchpad

RX FIFO Counter Mode

TX FIFO Counter Mode

RX FIFO Counter Mode

Alternate RX/TX FIFO
Counter Mode

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

4.14

Baud Rate Generator Registers (DLL and DLM) - Read/Write

The concatenation of the contents of DLM and DLL gives the 16-bit divisor value which is used to calculate the
baud rate:

Baud Rate = (Clock Frequency / 16) / Divisor

See MCR bit-7 and the baud rate table also.

4.15

Device Identification Register (DVID) - Read Only

This register contains the device ID (0x0A for XR16C2752). Prior to reading this register, DLL and DLM should
be set to 0x00.

4.16

Device Revision Register (DREV) - Read Only

This register contains the device revision information. For example, 0x01 means revision A. Prior to reading
this register, DLL and DLM should be set to 0x00.

4.17

Trigger Level Register (TRG) - Write-Only

User Programmable Transmit/Receive Trigger Level Register.

TRG[7:0]: Trigger Level Register

These bits are used to program desired trigger levels when trigger Table-D is selected. FCTR bit-7 selects
between programming the RX Trigger Level (a logic 0) and the TX Trigger Level (a logic 1).

4.18

RX/TX FIFO Level Count Register (FC) - Read-Only

This register is accessible when LCR = 0xBF. Note that this register is not identical to the FIFO Level Count
Register which is located in the general register set when FCTR bit-6 = 1 (Scratchpad Register Swap). It is
suggested to read the FIFO Level Count Register at the Scratchpad Register location when FCTR bit-6 = 1.
See

Table 12

FC[7:0]: RX/TX FIFO Level Count

Receive/Transmit FIFO Level Count. Number of characters in Receiver FIFO (FCTR[7] = 0) or Transmitter
FIFO (FCTR[7] = 1) can be read via this register.

4.19

Feature Control Register (FCTR) - Read/Write

This register controls the XR16L2752 new functions.

FCTR[1:0]: RTS Hysteresis

User selectable RTS# hysteresis levels for hardware flow control application. After reset, these bits are set to
"0" to select the next trigger level for hardware flow control. See

Table 13 on page 19

for more details.

FCTR[2]: IrDa RX Inversion

Logic 0 = Select RX input as encoded IrDa data.

Logic 1 = Select RX input as active high encoded IrDa data.

FCTR[3]: Auto RS-485 Direction Control

Logic 0 = Standard ST16C550 mode. Transmitter generates an interrupt when transmit holding register
becomes empty and transmit shift register is shifting data out.

Logic 1 = Enable Auto RS485 Direction Control function. The direction control signal, RTS# pin, changes its
output logic state from LOW to HIGH one bit time after the last stop bit of the last character is shifted out.
Also, the Transmit interrupt generation is delayed until the transmitter shift register becomes empty. The
RTS# output pin will automatically return LOW when a data byte is loaded into the TX FIFO. However, RTS#
behavior can be inverted by setting EMSR[3] = 1.

XR16L2752

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.2.0

EFR[4]: Enhanced Function Bits Enable

Enhanced function control bit. This bit enables IER bits 4-7, ISR bits 4-5, FCR bits 4-5, and MCR bits 5-7 to be
modified. After modifying any enhanced bits, EFR bit-4 can be set to a logic 0 to latch the new values. This
feature prevents legacy software from altering or overwriting the enhanced functions once set. Normally, it is
recommended to leave it enabled, logic 1.

Logic 0 = modification disable/latch enhanced features. IER bits 4-7, ISR bits 4-5, FCR bits 4-5, and MCR
bits 5-7 are saved to retain the user settings. After a reset, the IER bits 4-7, ISR bits 4-5, FCR bits 4-5, and
MCR bits 5-7 are set to a logic 0 to be compatible with ST16C550 mode (default).

Logic 1 = Enables the above-mentioned register bits to be modified by the user.

EFR[5]: Special Character Detect Enable

Logic 0 = Special Character Detect Disabled (default).

Logic 1 = Special Character Detect Enabled. The UART compares each incoming receive character with
data in Xoff-2 register. If a match exists, the receive data will be transferred to FIFO and ISR bit-4 will be set
to indicate detection of the special character. Bit-0 corresponds with the LSB bit of the receive character. If
flow control is set for comparing Xon1, Xoff1 (EFR [1:0]= `10') then flow control and special character work
normally. However, if flow control is set for comparing Xon2, Xoff2 (EFR[1:0]= `01') then flow control works
normally, but Xoff2 will not go to the FIFO, and will generate an Xoff interrupt and a special character
interrupt, if enabled via IER bit-5.

ABLE

15: S

OFTWARE

LOW

ONTROL

UNCTIONS

EFR

BIT

-3

ONT

-3

EFR

BIT

-2

ONT

-2

EFR

BIT

-1

ONT

-1

EFR

BIT

-0

ONT

-0

RANSMIT

AND

ECEIVE

OFTWARE

LOW

ONTROL

No TX and RX flow control (default and reset)

No transmit flow control

Transmit Xon1, Xoff1

Transmit Xon2, Xoff2

Transmit Xon1 and Xon2, Xoff1 and Xoff2

No receive flow control

Receiver compares Xon1, Xoff1

Receiver compares Xon2, Xoff2

Transmit Xon1, Xoff1

Receiver compares Xon1 or Xon2, Xoff1 or Xoff2

Transmit Xon2, Xoff2

Receiver compares Xon1 or Xon2, Xoff1 or Xoff2

Transmit Xon1 and Xon2, Xoff1 and Xoff2,

Receiver compares Xon1 and Xon2, Xoff1 and Xoff2

No transmit flow control,

Receiver compares Xon1 and Xon2, Xoff1 and Xoff2

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

Test 1: The following inputs must remain steady at VCC or GND state to minimize Sleep current: A0-A2, D0-
D7, IOR#, IOW#, CS#, CHSEL, and all modem inputs. Also, RXA and RXB inputs must idle at logic 1 state
while asleep. Floating inputs will result in sleep currents in the mA range. For PowerSave feature that isolates
address, data and control signals, please see the XR16L2751 datasheet.

ABSOLUTE MAXIMUM RATINGS

Power Supply Range

7 Volts

Voltage at Any Pin

GND-0.3 V to 7 V

Operating Temperature

-40

to +85

Storage Temperature

-65

to +150

Package Dissipation

500 mW

TYPICAL PACKAGE THERMAL RESISTANCE DATA

(MARGIN OF ERROR: ± 15%)

Thermal Resistance (44-PLCC)

theta-ja = 50

C/W, theta-jc = 21

C/W

ELECTRICAL CHARACTERISTICS

DC ELECTRICAL CHARACTERISTICS

NLESS

OTHERWISE

NOTED

: TA=0

C (-40

+85

FOR

INDUSTRIAL

GRADE

PACKAGE

), V

=2.25 -5.5V

YMBOL

ARAMETER

IMITS

2.5V

IMITS

3.3V

IMITS

5.0V

NITS

ONDITIONS

ILCK

Clock Input Low Level

-0.3

0.6

-0.3

0.6

-0.5

0.6

IHCK

Clock Input High Level

2.0

VCC

2.4

VCC

3.0

VCC

Input Low Voltage

-0.3

0.8

-0.3

0.8

-0.5

0.8

Input High Voltage

2.0

5.5

2.0

5.5

2.2

5.5

Output Low Voltage

0.4

= 6 mA

= 4 mA

= 2 mA

Output High Voltage

1.8

2.0

2.4

= -6 mA

= -1 mA

= -400 uA

Input Low Leakage Current

±10

Input High Leakage Current

±10

Input Pin Capacitance

Power Supply Current

2.7

SLEEP

Sleep Current

See Test 1

XR16L2752

REV. 1.2.0

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

NOTICE

EXAR Corporation reserves the right to make changes to the products contained in this publication in order to
improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any
circuits described herein, conveys no license under any patent or other right, and makes no representation that
the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration
purposes and may vary depending upon a user's specific application. While the information in this publication
has been carefully checked; no responsibility, however, is assumed for inaccuracies.

EXAR Corporation does not recommend the use of any of its products in life support applications where the
failure or malfunction of the product can reasonably be expected to cause failure of the life support system or
to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless
EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has
been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately
protected under the circumstances.

Datasheet August 2004.

Send your UART technical inquiry with technical details to hotline:

uarttechsupport@exar.com

Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.

REVISION HISTORY

ATE

EVISION

ESCRIPTION

November 2001

Rev P1.0.0

Prelim data sheet.

March 2002

Rev P1.1.0

Corrected INTA/B pin descriptions and reset state. Renamed Sclk to Bclk. Changed
A0-A7 in

Figures 16 and 17

to A0-A2.

September 2002

Rev 1.0.0

Release into production. Clarified RTS# pin descriptions, XTAL1 pin description,
external clock description, auto RS485 half-duplex control description, EMSR bit-3
description and updated 2.5 V, I

and I

SLEEP

DC Electrical Characteristics.

March 2003

Rev 1.1.0

Updated AC Electrical Characteristics.

August 2004

Rev 1.2.0

Added Device Status to Ordering Information. Clarified pin descriptions- changed
from using logic 1 and logic 0 to HIGH (VCC) and LOW (GND) for input and output
pin descriptions.

XR16L2750

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.1.0

TABLE OF CONTENTS

GENERAL DESCRIPTION .................................................................................................1

PPLICATIONS

.............................................................................................................................................1

EATURES

...................................................................................................................................................1

IGURE

1. XR16L2752 B

LOCK

IAGRAM

................................................................................................................................................. 1

IGURE

2. P

SSIGNMENT

............................................................................................................................................................. 2

ORDERING

INFORMATION

..............................................................................................................................2

PIN DESCRIPTIONS .........................................................................................................3

1.0 Product DESCRIPTION ........................................................................................................... 6
2.0 FUNCTIONAL DESCRIPTIONS .............................................................................................. 7

2.1 CPU I

NTERFACE

................................................................................................................................. 7

2.2 5-V

OLT

OLERANT

NPUTS

................................................................................................................... 7

2.3 D

EVICE

ESET

.................................................................................................................................... 7

2.4 D

EVICE

DENTIFICATION

AND

EVISION

................................................................................................. 7

2.5 C

HANNEL

AND

B S

ELECTION

............................................................................................................. 7

IGURE

3. XR16L2750 D

ATA

NTERCONNECTIONS

........................................................................................................................... 7

2.6 C

HANNEL

AND

B I

NTERNAL

EGISTERS

............................................................................................. 8

2.7 S

IMULTANEOUS

RITE

HANNEL

AND

B ...................................................................................... 8

2.8 DMA M

ODE

........................................................................................................................................ 8

ABLE

1: C

HANNEL

AND

B S

ELECT

....................................................................................................................................................... 8

ABLE

2: TXRDY#

AND

RXRDY# O

UTPUTS

FIFO

AND

DMA M

ODE

.................................................................................................... 8

2.9 INTA

AND

INTB O

UTPUTS

................................................................................................................... 9

2.10 C

RYSTAL

SCILLATOR

XTERNAL

LOCK

NPUT

............................................................................ 9

ABLE

3: INTA

AND

INTB P

INS

PERATION

FOR

RANSMITTER

................................................................................................................ 9

ABLE

4: INTA

AND

INTB P

PERATION

ECEIVER

....................................................................................................................... 9

IGURE

4. T

YPICAL

OSCILLATOR

CONNECTIONS

........................................................................................................................................ 9

2.11 P

ROGRAMMABLE

AUD

ATE

ENERATOR

....................................................................................... 10

IGURE

5. E

XTERNAL

LOCK

ONNECTION

FOR

XTENDED

ATA

ATE

................................................................................................. 10

IGURE

6. B

AUD

ATE

ENERATOR

AND

RESCALER

............................................................................................................................. 10

2.12 T

RANSMITTER

.................................................................................................................................. 11

2.12.1 Transmit Holding Register (THR) - Write Only ....................................................................................... 11
2.12.2 Transmitter Operation in non-FIFO Mode .............................................................................................. 11

ABLE

5: T

YPICAL

DATA

RATES

WITH

14.7456 MH

CRYSTAL

EXTERNAL

CLOCK

.............................................................................. 11

2.12.3 Transmitter Operation in FIFO Mode...................................................................................................... 12

2.13 R

ECEIVER

....................................................................................................................................... 12

IGURE

7. T

RANSMITTER

PERATION

NON

-FIFO M

ODE

...................................................................................................................... 12

IGURE

8. T

RANSMITTER

PERATION

FIFO

AND

LOW

ONTROL

ODE

............................................................................................. 12

2.13.1 Receive Holding Register (RHR) - Read-Only ....................................................................................... 13

IGURE

9. R

ECEIVER

PERATION

NON

-FIFO M

ODE

........................................................................................................................... 13

IGURE

10. R

ECEIVER

PERATION

FIFO

AND

UTO

RTS F

LOW

ONTROL

ODE

............................................................................... 13

2.14 A

UTO

RTS (H

ARDWARE

) F

LOW

ONTROL

........................................................................................ 14

2.15 A

UTO

RTS H

YSTERESIS

................................................................................................................. 14

2.16 A

UTO

CTS F

LOW

ONTROL

............................................................................................................ 14

IGURE

11. A

UTO

RTS

AND

CTS F

LOW

ONTROL

PERATION

.............................................................................................................. 15

2.17 A

UTO

OFF

OFTWARE

) F

LOW

ONTROL

................................................................................ 16

2.18 S

PECIAL

HARACTER

ETECT

........................................................................................................ 16

2.19 A

UTO

RS485 H

ALF

DUPLEX

ONTROL

............................................................................................ 16

ABLE

6: A

UTO

OFF

OFTWARE

) F

LOW

ONTROL

....................................................................................................................... 16

2.20 I

NFRARED

ODE

............................................................................................................................. 17

IGURE

12. I

NFRARED

RANSMIT

ATA

NCODING

AND

ECEIVE

ATA

ECODING

................................................................................. 17

2.21 S

LEEP

ODE

WITH

UTO

AKE

-U

................................................................................................ 18

2.22 I

NTERNAL

OOPBACK

...................................................................................................................... 19

IGURE

13. I

NTERNAL

OOP

ACK

HANNEL

AND

B ........................................................................................................................ 19

3.0 UART INTERNAL REGISTERS ............................................................................................. 20

ABLE

7: UART CHANNEL A AND B UART INTERNAL REGISTERS .............................................................................................. 20

ABLE

8: INTERNAL REGISTERS DESCRIPTION. S

HADED

BITS

ARE

ENABLED

WHEN

EFR B

-4=1 ................................................ 21

XR16L2750

2.25V TO 5.5V DUART WITH 64-BYTE FIFO

REV. 1.1.0

4.0 INTERNAL Register descriptions ........................................................................................ 22

4.1 R

ECEIVE

OLDING

EGISTER

(RHR) - R

EAD

- O

NLY

........................................................................... 22

4.2 T

RANSMIT

OLDING

EGISTER

(THR) - W

RITE

-O

NLY

......................................................................... 22

4.3 I

NTERRUPT

NABLE

EGISTER

(IER) - R

EAD

RITE

.......................................................................... 22

4.3.1 IER versus Receive FIFO Interrupt Mode Operation ............................................................................... 23
4.3.2 IER versus Receive/Transmit FIFO Polled Mode Operation.................................................................... 23

4.4 I

NTERRUPT

TATUS

EGISTER

(ISR) - R

EAD

-O

NLY

............................................................................ 24

4.4.1 Interrupt Generation: ................................................................................................................................ 24
4.4.2 Interrupt Clearing: .................................................................................................................................... 24

4.5 FIFO C

ONTROL

EGISTER

(FCR) - W

RITE

-O

NLY

............................................................................... 25

ABLE

9: I

NTERRUPT

OURCE

AND

RIORITY

EVEL

............................................................................................................................... 25

4.6 L

INE

ONTROL

EGISTER

(LCR) - R

EAD

RITE

................................................................................ 27

ABLE

10: T

RANSMIT

AND

ECEIVE

FIFO T

RIGGER

ABLE

AND

EVEL

ELECTION

.................................................................................. 27

ABLE

11: P

ARITY

SELECTION

................................................................................................................................................................ 28

4.7 A

LTERNATE

UNCTION

EGISTER

(AFR) - R

EAD

RITE

..................................................................... 29

4.8 M

ODEM

ONTROL

EGISTER

(MCR)

ENERAL

URPOSE

UTPUTS

ONTROL

- R

EAD

RITE

....... 29

4.9 L

INE

TATUS

EGISTER

(LSR) - R

EAD

NLY

..................................................................................... 30

4.10 M

ODEM

TATUS

EGISTER

(MSR) - R

EAD

NLY

............................................................................. 31

4.11 S

CRATCH

EGISTER

(SPR) - R

EAD

RITE

............................................................................... 32

4.12 E

NHANCED

ODE

ELECT

EGISTER

(EMSR) ................................................................................. 32

ABLE

12: S

CRATCHPAD

WAP

ELECTION

............................................................................................................................................ 32

4.13 FIFO L

EVEL

EGISTER

(FLVL) - R

EAD

-O

NLY

.................................................................................. 33

ABLE

13: RTS H

YSTERESIS

EVELS

.................................................................................................................................................... 33

4.14 B

AUD

ATE

ENERATOR

EGISTERS

(DLL

AND

DLM) - R

EAD

RITE

.............................................. 34

4.15 D

EVICE

DENTIFICATION

EGISTER

(DVID) - R

EAD

NLY

................................................................. 34

4.16 D

EVICE

EVISION

EGISTER

(DREV) - R

EAD

NLY

......................................................................... 34

4.17 T

RIGGER

EVEL

EGISTER

(TRG) - W

RITE

-O

NLY

............................................................................ 34

4.18 RX/TX FIFO L

EVEL

OUNT

EGISTER

(FC) - R

EAD

-O

NLY

.............................................................. 34

4.19 F

EATURE

ONTROL

EGISTER

(FCTR) - R

EAD

RITE

..................................................................... 34

ABLE

14: T

RIGGER

ABLE

ELECT

....................................................................................................................................................... 35

ABLE

15: S

OFTWARE

LOW

ONTROL

UNCTIONS

............................................................................................................................... 36

4.20 S

OFTWARE

LOW

ONTROL

EGISTERS

(XOFF1, XOFF2, XON1, XON2) - R

EAD

RITE

............... 37

ABLE

16: UART RESET CONDITIONS FOR CHANNEL A AND B ................................................................................................... 38

ABSOLUTE MAXIMUM RATINGS .................................................................................. 39
TYPICAL PACKAGE THERMAL RESISTANCE DATA (MARGIN OF ERROR: ± 15%) 39
ELECTRICAL CHARACTERISTICS................................................................................ 39

DC E

LECTRICAL

HARACTERISTICS

........................................................................................................... 39

AC E

LECTRICAL

HARACTERISTICS

........................................................................................................... 40

Unless otherwise noted: TA=0o to 70oC (-40o to +85oC for industrial grade package), Vcc=2.25-5.5V, ......... 40
70 pF load where applicable .............................................................................................................................. 40

IGURE

14. C

LOCK

IMING

.................................................................................................................................................................... 41

IGURE

15. M

ODEM

NPUT

UTPUT

IMING

HANNELS

A & B......................................................................................................... 41

IGURE

16. D

ATA

EAD

IMING

..................................................................................................................................................... 42

IGURE

17. D

ATA

RITE

IMING

.................................................................................................................................................... 42

IGURE

18. R

ECEIVE

EADY

& I

NTERRUPT

IMING

-FIFO M

ODE

]

FOR

HANNELS

A & B................................................................. 43

IGURE

19. T

RANSMIT

EADY

& I

NTERRUPT

IMING

-FIFO M

ODE

]

FOR

HANNELS

A & B............................................................... 43

IGURE

20. R

ECEIVE

EADY

& I

NTERRUPT

IMING

[FIFO M

ODE

, DMA D

ISABLED

]

FOR

HANNELS

A & B ............................................... 44

IGURE

21. R

ECEIVE

EADY

& I

NTERRUPT

IMING

[FIFO M

ODE

, DMA E

NABLED

]

FOR

HANNELS

A & B ................................................ 44

IGURE

22. T

RANSMIT

EADY

& I

NTERRUPT

IMING

[FIFO M

ODE

, DMA M

ODE

ISABLED

]

FOR

HANNELS

A & B ................................... 45

IGURE

23. T

RANSMIT

EADY

& I

NTERRUPT

IMING

[FIFO M

ODE

, DMA M

ODE

NABLED

]

FOR

HANNELS

A & B.................................... 45

PACKAGE DIMENSIONS (44 PIN PLCC) ....................................................................... 46

EVISION

ISTORY

.................................................................................................................................... 47

TABLE OF CONTENTS ................................................................................................................................. I

Document Outline

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: XR16L2752

Document Outline

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: XR16L2752