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2
2.9.2
2307 Serial Connections
The 2307's serial connector, J3, contains a three-line RS-232 interface, a
four-wire RS-485 interface and two bias voltages. RS-232 and RS-422
signal selection is made by setting jumpers on the 2307 board as shown in
Figures 2-7a and 2-7b and in Table 2-2. Signal-pin assignments for
connector J3 are listed in Table 2-3.
The 2307's RS-232 signals are wired as a DCE (Data Communication
Equipment) interface for direct connection to a PC's COM port. The RS-
232 interface is a three-wire interface with TX, RX and Ground signals. A
null-modem cable is not required to connect the 2307 to a PC. Bias signals
on the connector provide a true CTS signal level to the PC if the cable carries
the CTS signal.
The 2307's RS-485 signals are a TX and a RX data pair that meet the RS-
485 specification and can be used for two or four wire connections. Jumpers
on the board select RS-422/RS-485 signals and full or half-duplex operation.
For a point-to-point RS-422 connection, set the jumpers for RS-422 and
full-duplex. Use the SYST:COM:SER:RS485 command to turn off the
RS485 mode so the transmitter is enabled at all times.
For RS-422 party line or for RS-485 two wire operation, set the jumpers for
RS-422 and half-duplex. Use the SYST:COM:SER:RS485 command to
enable the RS485 mode so the transmitter will be tristated when it is not
transmitting. If the 2307 is at the end of the serial line, connect the bias
voltage pins to the data lines to keep the lines in the mark state when the
transmitters are tristated.
2.9.2.1 Example RS-422 Connections
The 2307's RS-422 signals can be connected to a PC's COM port through
an RS-232 to RS-422/RS-485 Converter. Figure 2-8 shows a four wire, full-
duplex connection using an ICS DataCom Model 485F Converter that plugs
directly to a PC's COM port. The wiring diagram includes pullup and
pulldown resistors so the 2307 can be operated with the 2307's RS485 mode
enabled or disabled.
