ST68C554 datasheet(9/40 Pages) EXAR

9 / 40 page

ST16C554/554D/68C554

Rev. 3.10

SYMBOL DESCRIPTION

Symbol

Signal

Pin Description

type

XTAL1

Crystal or External Clock Input - Functions as a crystal input

or as an external clock input. A crystal can be connected

between this pin and XTAL2 to form an internal oscillator

circuit (see figure 8). Alternatively, an external clock can be

connected to this pin to provide custom data rates (see

Baud Rate Generator Programming).

XTAL2

Output of the Crystal Oscillator or Buffered Clock - (See also

XTAL1). Crystal oscillator output or buffered clock output.

-CD A-B

9,27

64,18

-CD C-D

43,61

31,49

Carrier Detect (active low) - These inputs are associated

with individual UART channels A through D. A logic 0 on this

pin indicates that a carrier has been detected by the modem

for that channel.

-CTS A-B

11,25

2,16

-CTS C-D

45,59

33,47

Clear to Send (active low) - These inputs are associated with

individual UART channels, A through D. A logic 0 on the -

CTS pin indicates the modem or data set is ready to accept

transmit data from the 554D. Status can be tested by

reading MSR bit-4.

-DSR A-B

10,26

1,17

-DSR C-D

44,60

32,48

Data Set Ready (active low) - These inputs are associated

with individual UART channels, A through D. A logic 0 on

this pin indicates the modem or data set is powered-on and

is ready for data exchange with the UART. This pin has no

effect on the UARTs transmit or receive operation. This pin

has no effect on the UARTs transmit or receive operation.

-DTR A-B

12,24

3,15

-DTR C-D

46,58

34,46

Data Terminal Ready (active low) - These inputs are

associated with individual UART channels, A through D. A

logic 0 on this pin indicates that the 554D is powered-on and

ready. This pin can be controlled via the modem control

output to logic 0, enabling the modem. This pin will be a logic

1 after writing a logic 0 to MCR bit-0. This pin has no effect

on the UARTs transmit or receive operation.

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