ST68C554 datasheet(6/40 Pages) EXAR

6 / 40 page

ST16C554/554D/68C554

Rev. 3.10

SYMBOL DESCRIPTION

Symbol

Signal

Pin Description

type

-CS A-B

16,20

7,11

-CS C-D

50,54

38,42

Chip Select A, B, C, D (active low) - This function is

associated with the 16 mode only, and for individual chan-

nels, A through D. When in 16 Mode, these pins enable

data transfers between the user CPU and the ST16C554D

for the channel(s) addressed. Individual UART sections (A,

B, C, D) are addressed by providing a logic 0 on the

respective -CS A-D pin. When the 68 mode is selected, the

functions of these pins are reassigned. 68 mode functions

are described under the their respective name/pin head-

ings.

D0-D2

66-68

53-55

I/O

D3-D7

1-5

56-60

Data Bus (Bi-directional) - These pins are the eight bit, three

state data bus for transferring information to or from the

controlling CPU. D0 is the least significant bit and the first

data bit in a transmit or receive serial data stream.

GND

6,23

14,28

GND

40,57

45,61

Pwr

Signal and power ground.

INT A-B

15,21

6,12

INT C-D

49,55

37,43

Interrupt A, B, C, D (active high) - This function is associated

with the 16 mode only. These pins provide individual

channel interrupts, INT A-D. INT A-D are enabled when

MCR bit-3 is set to a logic 1, interrupts are enabled in the

interrupt enable register (IER), and when an interrupt con-

dition exists. Interrupt conditions include: receiver errors,

available receiver buffer data, transmit buffer empty, or

when a modem status flag is detected. When the 68 mode

is selected, the functions of these pins are reassigned. 68

mode functions are described under the their respective

name/pin headings.

INTSEL

Interrupt Select. (active high, with internal pull-down) - This

function is associated with the 16 mode only. When the 16

mode is selected, this pin can be used in conjunction with

MCR bit-3 to enable or disable the three state interrupts, INT

A-D or override MCR bit-3 and force continuous interrupts.

Interrupt outputs are enabled continuously by making this

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