SmartSwarm 300 Series
:
40
2
RTS
Input
3
GND
—
4
RXD
Input
5
TXD
Output
Table 10. RS-232 pinout
In order to operate on RS-232 based Modbus RTU networks, it is necessary to arrange for the SmartSwarm 351 to
receive information from both the RS-232 Transmit and Receive signals, in order that it can monitor both the
Modbus commands and the corresponding replies.
RS-232 data taps, B+B part number 9PCDT (9 pin) or 25PCDT (25 pin) are available for this purpose. The following
description assumes the use of the 9 pin version.
The device should be inserted into the RS-232 communications line between the Modbus master and slave.
Switches 1 & 2 should both be ON in order to pass both Rx and Tx data. In addition, switch 3 should be ON and
switch 4 OFF. Connections should then be made between the data tap pin 5 and the SmartSwarm RS-232
connector pin 3, and the data tap pin 2 and the SmartSwarm RS-232 connector pin 4. No other connections are
necessary.
The following image shows the correct configuration of DIP switches:
4.5.3 WIRE RS-485 AND RS-422 CONNECTION
Please read Section 3.3.3.2 of the “Modbus Serial Line Protocol and Implementation Guide”
(Modbus_over_serial_line_V1_02.pdf), which covers “Compatibility between 4-Wire and 2-Wire cabling” (see
http://www.modbus.org/docs/Modbus_over_serial_line_V1_02.pdf
). The RS-485 interface of the SmartSwarm
351 is effectively a 2-wire interface. In order to connect a 4-wire system to the device, you have to short the
Transmit and Receive pairs together.