Vi-2-9. Printer Interface Circuit - Canon A-200 series Service Manual

VI-2-9. Printer Interface Circuit
Figure 6-16 shows the printer interface circuit. This circuit consists of two output latches (U42
and U49), three input buffers (U138, U139 and U64) and a decoder circuit which selects the
functions of these latches and buffers.
When the CPU assigns addresses 378 through 37FH as 1/0 addresses, a LOW level PTR
signal is sent to U 11 D. U 110 then makes each latch and buffer enable by decoding AD, A1,
10W-N and 10R-N signals.
Table 6-5 shows the definition for data bus at each 1/0 address. Figure 6-17 shows the timing
chart at printing.
Print Data
0-7
Latch
SEL
INIT
AUTO
STB
ERROR
SLCT
PE
ACK
A O > - - - - - 1 A
BUSY
A 1 > - - - - - t B
U110
IOW-N 1C
IOR-N
> - - - - . 0
2C
1G
PTR > - - -.....-Q2G
Figure 6-16
66