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M Z3f:i)O
3-3. Sub-CPU and I/O port
AS6
3
AS5
7
SUB
AS4
1
CPU
AS7
4
...
5
...
MT
6
lower
0
N
§
M
....
0
~
8
0
0
8
0
(1)
8
0 0
~
0
upper
~
~
AS 7654 MEX
0
1 2 3 4
5
0000
0
_ S O O
0001
1
-
501 8251
0010
2
S02 8253
0011
3
503 8255
7
Y7
C
9
Y6
B
10
Y5
A
11
4G
Y4
G2A
Y3
12
I~
G2B
Y2
14
Gl
YI
15
YO
74LSI38
0
....
0
~
8 ....
~
~
~ ~
0 0
0 0
~
....
6
7 8
9
A B
507
--"'
506
505
504
503
502
SOT
500
8
0
0
~
~
~
~
~
~
~
C 0
E
GI>C-I
Graphic option
Shown at the left
IS
the circuit used by
the CPU to select the I/O ports The out
put address from the sub CPU
IS
decoded
by the 74 LS 138 to create the sel eet signal.
Shown below is the address map and
select signals.
CSP-I.CSP-2
Input port select (LS244)
8255-CS
8253-CS
8251-CS
MAIN CPU·INT
....
~
~
Signal description
~
F
~
Output signal to set the flipflop to apply interrupt (INTO) to the
main CPU. Enables communication between CPU·s.
8251 510 chip select.
:!Io
ASO is used for data control selection.
AS1, AS2, and A53 are "don't care".
8253 counter chip select.
A50 and ASl are used for programming during write.
AS2 and A53 are "don't care".
8255 PlO chip select.
ASO and AS1 are used for port/control selection.
AS2 and A53 are "don't care".
8·bit input port.
0100
4
504 input port select
Used for read.
AS3 are "don't care".
CAT control 110 port chip select.
0101
5
505
AS1, AS2, and AS3 are used for write.
ASO is "don't care".
UP07220 (graphic) chip select.
0110
6
506
ASO is used for read and write.
ASl, AS2, and AS3 are "don't care".
UP07220 (character) chip select.
0111
7
507
ASO is used for read and write.
AS1, AS2, and AS3 are "don't care".
1000
8
~
/
1001
9
1010
A
1011
B
1100
C
NOT USE
1101
0
/
~
1110
E
1111
F
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