Sharp MZ-80B Owner's Manual page 59

50
The control contents of each port are listed below:
Table 4.3
PortA
Port
terminal
Active Control function
PA
7
H
Lights up LED for
[iivs)
PA
6
H Lights up LED for
r-GRPH )
PAs
H Lights up LED for
[sn
LocK)
PA
4
L
Reverses B/W of entire display screen.
PA
3
H Stops cassette operation.
PA
2
H Plays cassette.
PA
1
H
Makes ready for FF state (makes ready for REW with L).
PA
0
H
Reel motor ON.
Port B
Port
terminal
Active
Control function
PB
7
H Detects break key while playing cassette.
PB
6
Cassette reading data.
PBs
L
Cassette being set.
PB
4
L
Applies pawl for prohibiting writing of cassette tape.
PB
3
} Reserve input ports. PB
2
PB
1
PB
0
H
Blanking period of display.
Port C
Port
Active Control function
terminal
PC
7
Data to be written into cassette.
PC
6
H
Head amp setting to READ state (WRITE with L).
PCs
H Latches ready state for FF andREW.
PC
4
L
Eject operation.
PC
3
L IPL starts.
PC
2
Source pulse output for generating sound.
Pel
H Sets memory in normal state, starting $0000.
PC
0
H Forces display to be blank.