Epson LQ-2550 Technical Manual page 104

2.3.3.2 Switch Status
The state of each switch is read periodically by the sub CPU through analog ports AN5 to AN7. When
the state of a switch is found to be different from the previous value, the new value is transferred to
the LED drive and LCD control/drive sections as data to rewrite the switch status.
Since the states of 11 switches must be read using only the three input ports (AN5 to AN7), a matrix
circuit is constructed using four control signals (O 15 and 016 of the MSM59371, CKO, and DTO) (See
Table 2-34).
The state of the ON LINE switch is monitored using port PC3 of the sub CPU via LPF (consisting of R66
and C40).
M S M 5 9 3 7 1
0 1 6
1
o
o
0
NOTE:
Read Section
Table 2-34. Switch Status Reading
(OUT)
Control Signal Status
0 1 5
0 0
1 0
0 1
0 0
for the layout of the switches.
Refer to Table A-40
SUB CPU
(IN)
Switches Read
0
0
0 —
1
2-57