CMP82C55AZ datasheet(15/26 Pages) RENESAS

15 / 26 page

MS82C55A, MQ82C55A, MP82C55A

FN6140 Rev 2.00

Page 15 of 26

June 15, 2006

Reading Port C Status (Figures 15 and 16)

In Mode 0, Port C transfers data to or from the peripheral

device. When the 82C55A is programmed to function in Modes

1 or 2, Port C generates or accepts “hand shaking” signals with

the peripheral device. Reading the contents of Port C allows

the programmer to test or verify the “status” of each peripheral

device and change the program flow accordingly.

There is not a special instruction to read the status information

from Port C. A normal read operation of Port C is executed to

perform this function.

Applications of the 82C55A

The 82C55A is a very powerful tool for interfacing peripheral

equipment to the microcomputer system. It represents the

optimum use of available pins and is flexible enough to

interface almost any I/O device without the need for additional

external logic.

Each peripheral device in a microcomputer system usually has

a “service routine” associated with it. The routine manages the

software interface between the device and the CPU. The

functional definition of the 82C55A is programmed by the I/O

service routine and becomes an extension of the system

software. By examining the I/O devices interface

characteristics for both data transfer and timing, and matching

this information to the examples and tables in the detailed

operational description, a control word can easily be developed

to initialize the 82C55A to exactly “fit” the application. Figures

18 through 24 present a few examples of typical applications of

the 82C55A.

INTERRUPT

ENABLE FLAG

POSITION

ALTERNATE PORT C

PIN SIGNAL (MODE)

INTE B

PC2

ACKB (Output Mode 1)

or STBB (Input Mode 1)

INTE A2

PC4

STBA (Input Mode 1 or Mode 2)

INTE A1

PC6

ACKA (Output Mode 1 or Mode 2)

FIGURE 17. INTERRUPT ENABLE FLAGS IN MODES 1 AND 2

FIGURE 18. PRINTER INTERFACE

PA0

PA1

PA2

PA3

PA4

PA5

PA6

PA7

PC7

PC6

PC5

PC4

PB0

PB1

PB2

PB3

PB4

PB5

PB6

PB7

PC1

PC2

DATA READY

ACK

PAPER FEED

FORWARD/REV.

DATA READY

ACK

PAPER FEED

FORWARD/REV.

RIBBON

CARRIAGE SEN.

MODE 1

(OUTPUT)

82C55A

MODE 1

(OUTPUT)

CONTROL LOGIC

AND DRIVERS

INTERRUPT

REQUEST

PC0

INTERRUPT

REQUEST

PC3

HAMMER

RELAYS

HIGH SPEED

PRINTER

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