82C55 datasheet(17/23 Pages) INTEL

17 / 23 page

82C55A

Reading Port C Status

In Mode 0 Port C transfers data to or from the pe-

ripheral device When the 82C55A is programmed to

function in Modes 1 or 2 Port C generates or ac-

cepts ‘‘hand-shaking’’ signals with the peripheral de-

vice Reading the contents of Port C allows the pro-

grammer to test or verify the ‘‘status’’ of each pe-

ripheral device and change the program flow ac-

cordingly

There is no special instruction to read the status in-

formation from Port C A normal read operation of

Port C is executed to perform this function

INPUT CONFIGURATION

IO IO IBFA INTEA INTRA INTEB IBFB INTRB

GROUP A

GROUP B

OUTPUT CONFIGURATIONS

D5 D4

OBFA INTEA IO IO INTRA INTEB OBFB INTRB

GROUP A

GROUP B

Figure 17a MODE 1 Status Word Format

OBFA INTE1 IBFA INTE2 INTRA

GROUP A

GROUP B

(Defined By Mode 0 or Mode 1 Selection)

Figure 17b MODE 2 Status Word Format

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 18 Interrupt Enable Flags in Modes 1 and 2

82C55 Datasheet(PDF) 17 Page - Intel Corporation