User manual

105G Wireless Gateway User Manual
Elpro_man_105g_1.18.doc Page 70
4.7.2 MODBUS Master
If you use the 105G as a Modbus Master, then the host device/s will be Modbus Slave device/s.
If the RS485 port is used, then multiple Modbus Slave devices can be connected to the 105G.
The 105G Modbus Master will generate Modbus read and write commands to the Modbus Slave
devices.
First read the above section on Modbus Slave operation, for an understanding of how the 105G
handles Modbus registers, and the types of Modbus commands the 105G Master can generate.
The Modbus Master commands are configured in the “Serial Mapping” screen. The serial port is
configured in the same way as described in the above section on Modbus Slave.
To enter a Modbus command, select “New Serial Mapping”. The following example is a digital
write command which writes 105G I/O registers 20 – 25 (6 registers) to Modbus outputs 00012 –
00017, at Modbus Slave address 1.
The entry under “I/O Register” is the first I/O register in the 105G to be transferred - the “I/O
count” is the number of registers to be transferred. If the selected Modbus slave does not
respond to the command, then the 105G will write a ‘FFFF’ value to one of its own registers,
configured under “CF Register” - in this case it is register 4800.
The “Command Type” selected is a write command (you can select read or write) - which means
that the values are sent from the 105G to the Modbus Slave. The type of write command is a
“Digital” write, meaning that the register values will be written as digital/binary values”.