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MZ3500
3-3. Sub CPU and I/O port
SUB
CPU
AS6
5
ASS
2
AS4
i
AST
4_
*""
5
"MT
6
Y6
4G
Y 4
Gl
Yl
YO
74LS138
J
s07
*.
~9
S06
_JQ
SOS
^
J
r CKP 1 . CSP 2
.Jl
SO4 ^ .
.
. . . . . .
0
12
S03
,.
-^
D
15
S
°
2
HEC3 -C*
14
"SOT
-^
D
15
'*°° r MAIN CPU \m
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 74LS138to create the select signal.
Shown below is the address map and
select signals.
AS 7654
M
£X\
8
8
1
2 3 4 5 6 7 8 9 A B C D E F
8
8
Signal description
0000
soo
Output signal to set the flipflop to apply interrupt (INTO) to the
main CPU. Enables communication between CPU's.
0001
S01
8251
8251 SIO chip select.
ASO is used for data control selection.
AS1, AS2, and ASS are "don't care".
0010
S02 8253
8253 counter chip select.
ASO and AS1 are used for programming during write.
AS2 and ASS are "don't care".
0011
S03 8255
8255 PIO chip select.
ASO and AS1 are used for port/control selection.
AS2 and ASS are "don't care".
0100
S04 input port select
8-bit input port.
Used for read.
AS3 are "don't care".
0101
805
CRT control I/O port chip select.
AS1, AS2, and ASS are used for write.
ASO is "don't care".
0110
S06
UPD7220 (graphic) chip select.
ASO is used for read and write.
AS1, AS2, and AS3 are "don't care"
0111
S07
UPD7220 (character) chip select.
ASO is used for read and write.
AS1, AS2, and AS3 are "don't care"
1000
1001
1010
1011
1100
1101
1110
1111
NOT USE
- 18-
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