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M ! 3500
7-6. I/O
port map
8255 ON SUB CPU BUS
I'A7
1Nl
X
f - -
I'A6
OUT #3
f - -
I'A5
~
~
8255
~
(;)
~
chip address[OO11/xxxx)
0
c
"0
I
PAO
~
PC7
Group A: Mode 1
PC6
Group B: Mode 0
PC5
t - -
PC4
PC3
PC2
r-----
PCI
r-----
PCO
PB7
(;)
~
(3
t - -
c
PB5
"0
t - -
CJ
PB4
PB3
PB2
PBI
PBO
INPUT PORT ( 74LS244)
(DS7 )
74LS244
(DS6 )
port address[Ol00/xxxx]
(DS5 )
(Us4J
IN}# X
(DS3)
OUT
4
(DS2)
(DSI)
(DSO)
...
Output
OBF output
ACK input,
J
INTR
Output
HLT KEY
STK
]
DK
PUTR
J
PE
BUSY
I>ATA8
l
DATA7
IlATA6
I>ATA5
llATA4
DATA3
DATA2
DATAl
ACK
-r:
SET
ACK
STROBE
MU
SIC.
sustain
NOT USE
Printer
ACKC
STC
DC
PiM
SRDY
CLK
]
Keyboard
D10
C2
Cl
CO
STRB
Keyboard
Printer
CG
selectIon
Sub CPU READY
Clock
Reads the 8255 OBF (PC7)
output or timer output.
- 80-
,
I
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