Lexmark Printer User Manual page 370

DTR and DTR/DSR Protocol Timing (RS-232C)
Use DTR to pace the data flow from the computer. DTR goes from high to low to
indicate to the computer that the printer cannot receive more data when it detects the
following BUSY conditions:
The following diagram illustrates DTR Protocol Timing.
Legend:
1
2
3
4
•
Buffer full
•
Attendance error
•
Printer not in ready state
1
2
The RTS signal is driven active as long as power is supplied to the printer.
The DTR signal becomes active when initialization is complete, telling the computer that
the printer is ready to receive data.
When Honor DSR is On, the printer considers data received invalid when DSR is low
and discards the data. Only DTR/DSR is used for flow control from the printer to the host
computer.
DTR drops to tell the computer that the receive buffer is nearly full or that the printer is
busy and that data transmission should stop. About 640 free bytes remain in the buffer at
this time. If the computer continues to send data after the printer has sent a low DTR
signal, data could be lost.
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Interfaces
3
Receive Data Valid
4