82C55A Datasheet, PDF (17/23 Pages) Intel Corporation – CHMOS PROGRAMMABLE PERIPHERAL INTERFACE

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
D₇ D₆ D₅ D₄
D₃
D₂ D₁ D₀
I O I O IBF_A INTE_A INTR_A INTE_B IBF_B INTR_B
GROUP A
GROUP B
OUTPUT CONFIGURATIONS
D₇
D₆ D₅ D₄ D₃
D₂
D₁
D₀
OBF_A INTE_A I O I O INTR_A INTE_B OBF_B INTR_B
GROUP A
GROUP B
Figure 17a MODE 1 Status Word Format
D₇ D₆ D₅ D₄ D₃ D₂ D₁ D₀
OBF_A INTE₁ IBF_A INTE₂ INTR_A
GROUP A
(Defined By Mode 0 or Mode 1 Selection)
GROUP B
Figure 17b MODE 2 Status Word Format
Interrupt Enable Flag
Position
Alternate Port C Pin Signal (Mode)
INTE B
INTE A2
INTE A1
PC2
ACK_B (Output Mode 1) or STB_B (Input Mode 1)
PC4
STB_A (Input Mode 1 or Mode 2)
PC6
ACK_A (Output Mode 1 or Mode 2
Figure 18 Interrupt Enable Flags in Modes 1 and 2
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