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ST16C2552

REV. 4.2

2.97V TO 5.5V DUAL UART WITH 16-BYTE FIFO

7

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 2552 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

Device Reset

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

state (see the Table 11). An active high pulse of longer than 40 ns duration will be required to activate the reset

function in the device.

2.3

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.

CS#

CHSEL

1

X

UART de-selected

0

1

Channel A selected

0

0

Channel B selected

VCC

VCC

(OP2A#)

DSRA#

CTSA#

RTSA#

DTRA#

RXA

TXA

RIA#

CDA#

(OP2B#)

DSRB#

CTSB#

RTSB#

DTRB#

RXB

TXB

RIB#

CDB#

GND

A0

A1

A2

UART_CS#

UART_CHSEL

IOR#

IOW #

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

CS#

CHSEL

D0

D1

D2

D3

D4

D5

D6

D7

IOR#

IOW #

UART

Channel A

UART

Channel B

UART_INTB

UART_INTA

INTB

INTA

(RXRDYA#)

TXRDYA#

(RXRDYA#)

TXRDYA#

(RXRDYB#)

TXRDYB#

(RXRDYB#)

TXRDYB#

UART_RESET

RESET

Serial Interface of

RS-232, RS-485

Serial Interface of

RS-232, RS-485

2750int

(BAUDOUTB#)

(BAUDOUTA#)

Pins in parentheses become available through the MF# pin. MF# A/B becomes RXRDY# A/B when AFR[2:1] = '10'. MF# A/B becomes OP2# A/B

when AFR[2:1] = '00'. MF# A/B becomes BAUDOUT# A/B when AFR[1:0] = '01'.