THEORY OF OPERATION
2-1-2. RS422A interface
CN3
RD (+)
RD
CS (+)
CS
RS
RS (+)
SD
SD (+)
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| R2I | + |
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| D1O | B15 | B15 |
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| D2EN | A10 | A10 |
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| D2I | B12 | B12 |
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| D1I | B14 | B14 |
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IC10
Gate array
ERROR
ACK
IC5
CPU
RXD0
TXD0
RXD1
RS422A Interface PCB | Main PCB |
Fig. 2-3 RS422A Interface
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.)
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