105U-G Wireless Gateway
User Manual
Page
55
©
August 2003
Note that the same CF Register (“comms fail” register) has been used in the 105G. You can
use the same register or a different register in the range 4800 – 4999.
To complete the Data Bus Configuration, enter all of the Modbus commands required to
transfer I/O points between the 105G and the Modbus Slave devices.
Digital I/O
The value of a digital I/O point is stored in the 105G database as a hexadecimal '0000' (“off”) or
hex 'FFFF' (“on”). However the 105G will generate either a ‘0’ (“off”) or ‘1’ (“on”) to a digital
output point (Coil) when sending commands to a Modbus slave - these are commands 05 and 15.
Similarly, the 105G will accept ‘0’ or ‘1’ from the Modbus slave in response to a digital read
command and store ‘0000’ or ‘FFFF’ in the database location - these commands are 01 and 02.
Analogue I/O
Analogue I/O from the remote 105U modules are 16 bit register value. A value of 8192 (hex
2000) represents 0mA. A value of 49152 (hex C000) represents 20mA. Each mA has value of
2048 (hex 0800) - a change of 4096 (hex 1000) is equivalent to a change of 2mA. A 4-20mA
signal will vary between 16384 (hex 4000) and 49152 (hex C000). A 0-20mA signal will vary
between 8192 (hex 2000) and 49152 (hex C000).
Pulse I/O
Pulse counts from the remote 105U modules are shown as a 16-bit register. When the register
rolls over, from ‘FFFF’ (hex), the next value will be ‘0001’. The register will only have a
value of ‘0000’ when the remote module starts up, and the previous count is lost. This value
will indicate that the counter has reset.
Modbus Retry Delay
The 105G Modbus Master configuration includes a feature to limit the frequency at which slave
devices are polled for data. The 105G will poll each Modbus slave in order. If there is no delay
time entered, the 105G will poll as quickly as it is able to. If there is a delay time entered, then
this delay time will occur between each poll message.
