Rs422A - Star Micronics TSP400 Series Technical Manual

THEORY OF OPERATION
2-1-2. RS422A interface
CN3
RD (+)
RD (–)
CS (+)
CS (–)
RS (–)
RS (+)
SD (–)
SD (+)
IC1 operates as the RS422A driver and receiver.
Data flow from host to printer: IC1 receives serial data from the host computer via RD, converts the signal voltage from
RS422A level to TTL level, and passes the result to the CPU. The CPU converts the serial data to parallel and stores it
into buffer memory.
Data flow from printer to host: The CPU generates data, converts it into serial form, then passes it to IC1. IC1 converts
the signal voltage from TTL level to RS422A level, then outputs the result over the SD line.
The CS line is hardware-connected, but the connection is not recognized by software. (The printer does not monitor the
signal.)
IC1
+
R2I
+
–
R2I
–
+
R1I
+
–
R1I
–
D2O
D2O
D1O
D1O
MC34051
RS422A Interface PCB
Fig. 2-3 RS422A Interface
CN1 CN9
D2O A15 A15
D1O B15 B15
D2EN A10 A10
D2I B12 B12
D1EN
D1I B14 B14
– 22 –
IC10
Gate array
ERROR
ACK
IC5
CPU
RXD0
TXD0
RXD1
Main PCB