Real Time Devices AD1200 User Manual page 125

irfief
82C55A
Mode Deflnltlon Summary
PAo
PAr
PAz
PAs
P&
PAs
PAo
PAz
MODE O
IN
OUT
IN
IN
IN
IN
I N
IN
I N
I N
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
PBo
PBr
PBe
PBg
PBa
PBs
PBs
PBz
1N
I N
I N
IN
IN
I N
IN
IN
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
Pco
PCr
PCz
PCs
PCe
PCs
PCo
PCz
IN
IN
IN
IN
IN
I N
IN
I N
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
MODE 1
IN
ouT
IN
I N
IN
1N
I N
1N
I N
IN
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
IN
I N
IN
IN
I N
1N
I N
IN
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
INTRg
lBFs
ffia
INTRl
srEA
lBFa
l to
VO
INTRs
GFs
Affis
INTRa
alo
vo
TfKA
6EFa
MODE 2
GROUP A ONLY
<--.it
vo
t/o
llo
INTRI
sIBl
lBFa
Iffia
OtsF-a
MODE O
OH MODE 1
ONLY
Speclal Mode Comblnatlon Conslderailons
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 Mod6"
command.
During a read of Port C, the stat€ of all the port C
lines, except the Affi and SE lines, will be placed
on the data bus. In place of the Affi and ffi
line
states, flag status will appear on the data bus in the
PC2, PC/, and PCO bit positions as illustrated by
Figure 18.
Through a "Write Port G" command, only the Port C
pins programmed as outputs in a Mode 0 group can
be written. No other pins can be atfected 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
change an int€rrupt enable flag, the "Set/Reset Port
C Bit" command must be used.
With a "Set/Reset Port C Bit" command, any Port C
line plggrammed as an output (including |NTR, tBF
and OBF) can be written, or an interupt enable flag
can be €ither s€t or reset. Port C lines proqrammed
as inputs, inctuding Affi and SfB linei, aJsociated
with Port G are not atfected by a "Set/Reset Port C
Bit" command. Writing1]g the conesponding Port C
bit positions of the fiffi and SE'finei iritn tn"
"Set/Reset Port C Bit" command will atfect the
Group A and Group B interrupt enable flags, as illus.
trated in Figure 18.
Gurrent Drlve Capabltlty
Any output on Port A, B or C can sink or source 2.S
mA. This feature allows the 82Cf5A to direcily drive
Darlington bpe driv€rs and high-voltage displays
that require such sink or source current.
3-139