
GMS81508/16
51
Pin Function According to Operation Modes
PIN
Single Chip Mode
Microprocessor Mode
R20/A8
I/O
O
R21/A9
I/O
O
R22/A10
I/O
Programmable I/O Port
O
upper 8bit address of External Memory
R23/A11
I/O
O
for CPU.
R24/A12
I/O
O
R25/A13
I/O
O
R26/A14
I/O
O
R27/A15
I/O
O
3.4. R3 PORT
R3 Port is composed of 8-bit programmable I/O pin.
Register Name
Symbol
R/W
Address
Initial Value
R3 I/O Direction Register
R3DD
W
00C7
H
0000 0000
R3 PORT Data Register
R3
R/W
00C6
H
Not initialized
R3 PORT I/O DIRECTION REGISTER
R3 PORT DATA REGISTER
Determines I/O of R3 port
0 : Input
1 : Output
<00C7
H
>
R3DD
7
R3DD7
6
R3DD6
5
R3DD5
4
R3DD4
3
R3DD3
2
R3DD2
1
R3DD1
0
R3DD0
W
W
W
W
W
W
W
W
Port R3 output data
<00C6
H
>
R3
7
R37
6
R36
5
R35
4
R34
3
R33
2
R32
1
R31
0
R30
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W