THEORY OF OPERATION
2.Main and Interface PCBs
The main PCB and interface PCB provide the drive circuitry for the
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RS232C interface |
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| CN3 |
| CN1 | IC10 |
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| CN9 |
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| IC1 |
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| Gate array | IC5 |
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| D2O | D2I | B12 | B12 | CPU |
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| DTR |
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| ACK |
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| D1O | D1I | B14 | B14 | TXD0 |
| TXD |
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| R1I | R1O | A15 | A15 | RXD0 |
| RXD |
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| R2I | R2O | B15 | B15 | RXD1 |
| CTS |
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| HD151232FP |
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RS232C Interface PCB | Main PCB |
Fig. 2-2 RS232C Interface
Data flow from host to printer: IC1 receives serial data from the host computer via RXD, converts the signal voltage from RS232C 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 RS232C level, then outputs the result over the TXD line.
The CTS line is hardware-connected, but the connection is not recognized by software. (The printer does not monitor the signal.)
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