Modbus communication - GMW83 - GMW83A - GMW83D - GMW83DRP - GMW83DRPC - GMW83RPC - GMW84 - GMW84S - GMW86P - GMW87M

GMW80 Series User Guide

Document code
M211748EN
Revision
H
Language
English
Product
GMW83
GMW83A
GMW83D
GMW83DRP
GMW83DRPC
GMW83RPC
GMW84
GMW84S
GMW86P
GMW87M
Document type
User guide

The Modbus variant used in GMW87 is Modbus RTU. For a list of the Modbus registers available in GMW87, see Modbus registers.

You can use up to 8 transmitters on the same RS-485 line. You must configure each transmitter on the line to have a different Modbus address.

Before taking the transmitter into use, check that the Modbus device address, bit rate setting, and parity setting match the settings in your system.

The number of stop bits is not significant. The device supports automatically both 1 and 2 stop bits.

Figure 1. GMW87 component board with DIP switches and screw terminals
1
DIP switches for setting the GMW87 Modbus device address
2
DIP switches for selecting Modbus communication bit rate and parity (N/E)
3
Screw terminal not used in GMW87
4
DIP switch for 120 Ω RS-485 bus termination. Switch RS-485 bus termination ON only on the last device of the wiring if there is no separate terminator on the bus.
5
RS-485 (Modbus) screw terminals
6
Power supply input (18 … 35 VDC or 20 … 30 VAC) screw terminals

Make selections with the DIP switches by sliding the DIP switch to the right (ON). Keep the other DIP switches on the left position (OFF).

Setting Modbus device address with DIP switches

Figure 2. Modbus device address DIP switch example
DIP switches 32, 8, and 1 set to ON
The Modbus device address is encoded in eight bit binary form, with each numbered switch representing a single bit. This example shows address 41 selected: DIP switches 32, 8, and 1 (decimal: 41, binary: 00101001) are set to ON.

Modbus device address ranges

The Modbus device address range for the transmitter is 1 … 247. Up to 255 is possible, but non-standard.

If no address is selected (0), the device is off-line and will not respond to any Modbus requests.