Wiring nonsupported printers

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You might need to adapt your nonsupported printer so that it functions properly with the base operating system serial printer device driver.

The following table details what the RS-232 signals mean to the serial printer device driver:
RS-232 Signal Serial Printer Device Driver Use
FG Frame ground. Often used as shield.
TxD  —> Used to transmit data to printer.
RxD  <— Used to receive data from printer.
RTS  <— Held high after printer port opened. Provides host status to printer. Not used for data pacing.
CTS  <— Must be high for printer port to be opened. Used to detect that the printer is turned on.
DSR Not used. Usually tied to DCD.
SG Reference voltage for signals.
DCD  <— Used for data pacing when DTR is set to yes.
DTR  —> Held high after printer port opened. Provides host status to printer.
  1. If you use FG as a cable shield, make sure that it is connected only at one end. It makes no difference which end is connected. This provides an efficient shield against electrical noise.
  2. If your RTS signal is used to supply voltage to CTS on the printer port, check to see what your printer does with its RTS signal.

    Although RTS and CTS data pacing is not supported on serial printers, the device driver will block the open of the printer port until the voltage of CTS becomes high. The CTS signal is usually supplied by the RTS signal from the printer. However, some printers use the RTS signal for data pacing. These printers drop RTS when they want the system to stop sending data. Because the queuing system always needs the port opened to check for status, if the printer drops the RTS signal, the port closes and the queue goes down.

  3. Some printers require that you raise the voltage of DCD and DSR or CTS on the printer side. If your printer requires that these voltages be raised, use one of the following methods for raising the voltage:
    1. Use DTR or RTS on the computer side to supply the voltage.

      OR

    2. Obtain the voltage from the printer side.