Communications Operation 105
5.3.7 DTR/RTS Control Line
This additional outgoing signal operates independently of DSR/CTS operation. It is
commonly not used, but it may be necessary with some of modems or signal
converters.
With the DTR option selected, this signal is permanently asserted high.
When the RTS option is chosen, the signal is asserted high during transmission and
is low during reception. The Powermeter asserts the RTS line at least 10 ms before
the response message is sent out, and holds it asserted throughout the transmission.
NOTE
The DTR/RTS signal has an RS-232 bipolar logic level. When RS-422/485
communications is used, level conversion is necessary.
5.3.8 Configuring the Printer Parameters
When a serial printer is connected to the Powermeter, the print mode should be
selected, and baud rate and data format should be configured as those on the printer.
Cable connections to the printer may depend on the printer connector type. Most of
serial printers have a DTE 25-pin male connector, but some of them might have a
DCE 25-pin female connector. The cable drawings for both connector types are
shown in Appendix D.2.
Most of printers provide a few bytes of buffer storage where characters can wait
their turn to be printed. If the buffer size is sufficient to accept full print report, i.e.,
when a printer has at least 256 bytes of input buffer, flow control is not needed. If
the buffer size is less than 256 bytes, you should provide hardware handshaking,
otherwise the printer output will become garbled. Use the DSR/CTS signal to
provide hardware flow control. For the cable drawing, refer to Appendix D. In the
Powermeter, configure the handshaking parameter to HArd to make the Powermeter
to monitor DSR/CTS.
With a serial-to-parallel converter, you can use a parallel printer as well. When a
converter is used, hardware handshaking is required. Refer to Appendix D.2 for
cable drawings.
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