ST68C454 datasheet(5/30 Pages) EXAR

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ST16C454/68C454

Rev. 3.20

D0-D2

66-68

I/O

D3-D7

1-5

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

GND

40,57

Pwr

Signal and power ground.

INT A-B

15,21

INT C-D

49,55

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

the 16 mode only. These pins provide individual channel inter-

rupts, 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 condition exists. Interrupt conditions in-

clude: 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 pin a logic 1. Making this pin

a logic 0 allows MCR bit-3 to control the three state interrupt output.

In this mode, MCR bit-3 is set to a logic 1 to enable the three state

outputs. This pin is disabled in the 68 mode.

-IOR

Read strobe. (active low Strobe) - This function is associated with

the 16 mode only. A logic 0 transition on this pin will load the

contents of an Internal register defined by address bits A0-A2 onto

the ST16C454 data bus (D0-D7) for access by an external CPU.

This pin is disabled in the 68 mode.

-IOW

Write strobe. (active low strobe) - This function is associated with

the 16 mode only. A logic 0 transition on this pin will transfer the

contents of the data bus (D0-D7) from the external CPU to an

internal register that is defined by address bits A0-A2. When the

16 mode is selected, this pin functions as R/-W, see definition

Symbol

Signal

Pin Description

type

SYMBOL DESCRIPTION

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