82C55A Datasheet, PDF (16/23 Pages) Intel Corporation – CHMOS PROGRAMMABLE PERIPHERAL INTERFACE

82C55A
Mode Definition Summary
MODE 0
IN OUT
PA₀ IN OUT
PA₁ IN OUT
PA₂ IN OUT
PA₃ IN OUT
PA₄ IN OUT
PA₅ IN OUT
PA₆ IN OUT
PA₇ IN OUT
PB₀ IN OUT
PB₁ IN OUT
PB₂ IN OUT
PB₃ IN OUT
PB₄ IN OUT
PB₅ IN OUT
PB₆ IN OUT
PB₇ IN OUT
PC₀ IN OUT
PC₁ IN OUT
PC₂ IN OUT
PC₃ IN OUT
PC₄ IN OUT
PC₅ IN OUT
PC₆ IN OUT
PC₇ IN OUT
MODE 1
IN OUT
IN OUT
IN OUT
IN OUT
IN OUT
IN OUT
IN OUT
IN OUT
IN OUT
IN OUT
IN OUT
IN OUT
IN OUT
IN OUT
IN OUT
IN OUT
IN OUT
INTR_B
IBF_B
STB_B
INTR_A
STB_A
IBF_A
IO
IO
INTR_B
OBF_B
ACK_B
INTR_A
IO
IO
ACK_A
OBF_A
Special Mode Combination Considerations
There are several combinations of modes possible
For any combination some or all of the Port C lines
are used for control or status The remaining bits are
either inputs or outputs as defined by a ‘‘Set Mode’’
command
During a read of Port C the state of all the Port C
lines except the ACK and STB lines will be placed
on the data bus In place of the ACK and STB line
states flag status will appear on the data bus in the
PC2 PC4 and PC6 bit positions as illustrated by
Figure 18
Through a ‘‘Write Port C’’ command only the Port C
pins programmed as outputs in a Mode 0 group can
be written No other pins can be affected by a ‘‘Write
Port C’’ command nor can the interrupt enable flags
be accessed To write to any Port C output pro-
grammed as an output in a Mode 1 group or to
MODE 2
GROUP A ONLY
MODE 0
OR MODE 1
ONLY
IO
IO
IO
INTR_A
STB_A
IBF_A
ACK_A
OBF_A
change an interrupt enable flag the ‘‘Set Reset Port
C Bit’’ command must be used
With a ‘‘Set Reset Port C Bit’’ command any Port C
line programmed as an output (including INTR IBF
and OBF) can be written or an interrupt enable flag
can be either set or reset Port C lines programmed
as inputs including ACK and STB lines associated
with Port C are not affected by a ‘‘Set Reset Port C
Bit’’ command Writing to the corresponding Port C
bit positions of the ACK and STB lines with the
‘‘Set Reset Port C Bit’’ command will affect the
Group A and Group B interrupt enable flags as illus-
trated in Figure 18
Current Drive Capability
Any output on Port A B or C can sink or source 2 5
mA This feature allows the 82C55A to directly drive
Darlington type drivers and high-voltage displays
that require such sink or source current
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