User manual

Chapter Three Operation
Page 51 March 2010
WI-MOD-9-E with ModBus TCP to RTU Gateway enabled. Care should be taken to ensure that
the Device ID (i.e. ModBus Address) of the serial device is different to the Device ID of the
onboard ModBus TCP Server of the WI-MOD-9-E that the serial device is connected to.
The WI-MOD-9-E provides a configurable option to automatically reset the value of the onboard
I/O registers to zero in the event of a communications failure. If a valid ModBus transaction
directed to/from a given register has not been completed for longer than a configurable timeout,
then the value of that register will be reset to zero.
An example of the ModBus functionality of the WI-MOD-9-E is illustrated below. In this
example the status of the onboard digital input at C will be reflected at the onboard digital output
at B. Also, 8 I/O registers from ModBus serial device D will be transferred to A.
The ModBus configuration for unit C is shown below.
Unit C is configured with ModBus TCP Server enabled and Device ID = 1, so that the ModBus
TCP Client at B can connect and read the status of the onboard digital input. Unit C also has
ModBus TCP to RTU Gateway enabled (see section “3.13.3 ModBus TCP to RTU Gateway”) so
that the ModBus TCP Client at B can communicate with the serial ModBus RTU device D.
The configuration of unit B is shown below (accessible via the “I/O Transfer” configuration
page).
It can be seen that ModBus TCP Client has been enabled with a 500msec scan rate, meaning that
there will be a 500msec delay between each of the mappings directed at any server. The “Reset
Registers on Comms Fail” option is enabled with a timeout of 60 seconds, indicating that any of