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M / 3500
7-6. I/O port map
8255 ON SUB CPU BUS
I N
OUT
8255
chip address(0011/xxxxj
Group A: Mode 1
Group B: Mode 0
O
3
PA7
PA6
i'A5
I'A4
I'A3
PA2
PA1
PAO
PC7
PC6
PCS
PC4
PCS
PC 2
PCI
PCO
PB7
PB6
PBS
PB4
PBS
PB2
PB1
PBO
Output
OBF output
ACK inputi
1NTR
Output
DATA8
DATA"
DATA6
I) AT A 5
DATA4
DATA3
DATA2
DATA1
ACK T-SET
ACK
STROBE
J
MUS 1C , sustain
NOT USE
ACKC
STC
DC
P / M
SRDY
CLK
Printer
Dm
C2
C l
CO
STRB
Keyboard
CG selection
Sub CPU R E A D Y
Clock
INPUT P O R T C 7 4 L S 2 4 4
7 4 L S 2 4 4
port address[0100/xxxx]
I N
OUT
# 4 X
C D S 7 D
C D S 6 D
C D S 5 D
C D S 4 3
C D S 3 3
C D S 2 D
cosn
C D S O D
HLT KEY
STK
-i
DK
J
PUTR
PE
BUSY
Reads the 8255 OBF (PC7)
output or timer output.
Keyboard
Printer
- 80-
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