User`s guide

2-22
Guide to Printers and Printing
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.
2. If you use FG as a cable shield, make sure that it is only connected at one end. It makes
no difference which end is connected. This provides an efficient shield against electrical
noise.
3. 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. Since 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.
4. Some printers require that you raise the voltage of DCD and DSR or CTS on the printer
side. There are several methods for raising the voltage:
– Use DTR or RTS on the computer side to supply the voltage.
OR
– Obtain the voltage from the printer side.