User manual

Chapter 4 Configuration
Page 71 ©February 2009
If the Modbus Slave device does not respond to the Modbus command, the 105G will try another
3 times (“Max Retries” = 3). The Modbus command will be sent to the Modbus Slave every
100msec. The address of the Modbus Slave is 1 (permissible addresses are 1 – 255). Because a
digital write command has been selected, the destination register type will be digital outputs,
with Modbus tag “0xxxxx”. The first destination Modbus location is 12 (or 00012) - as there are
6 registers transferred, the destination locations will be 00012 – 00017.
The second example is a register read command to the same Modbus Slave (address 1). The
command requests the Modbus Slave to return the values of 10 registers which will be stored in
I/O registers 463 - 473 in the 105G. As the command is a “register read” command, the target
Modbus locations will be of the type 3xxxx. The starting location is 30001. So the values of
locations 30001 – 30010 in Modbus Slave 1 will be transferred to I/O registers 463 – 473 in the
105G.
The CF Register (“comms fail” register) acts as a digital alarm – the value of the register will
normally be 0, and will be set to FFFF (hex) if the slave device does not positively respond to the
serial command within Max Retries attempts. In the examples, the same CF Register (4327 – i.e.
DOT8) has been used for both serial mappings, such that the local digital output will be activated
if the slave fails to respond to either serial command. Alternately, any other internal register
could have been chosen and mapped via radio if desired.