User manual

WI-MOD-9-E Wireless Ethernet User Manual
WI-MOD-9-E Manual V1.9 Page 52
the registers at unit B will be reset if a successful ModBus transaction involving that register has
not been executed in the last 60 seconds. The ModBus TCP to RTU Gateway at B must also be
enabled (see section “3.13.3 ModBus TCP to RTU Gateway”) to allow ModBus communications
with the serial device A.
Three “ModBus TCP Client Mappings” are also configured at B in order to perform the required
I/O transfer. The first mapping transfers the status of the onboard digital input at C to the
onboard digital output at B. Local Register 4320 specifies the register for the onboard digital
output at B (since B is the local unit at which the mapping is configured). I/O Count 1 specifies
that only one I/O point is being transferred (i.e. the single digital I/O). Function Code 02: Read
Discretes specifies the standard ModBus function code to read discrete (i.e. digital) inputs.
Destination Register 4300 specifies the register for the onboard digital input at unit C (since C is
the destination unit for this mapping). Device ID 1is the ID of the onboard ModBus TCP Server
at C. Server IP Address 192.168.0.200 is the IP address of unit C – which is the ModBus TCP
Server we are reading from. Response Timeout 1000 ms specifies that unit C must respond to this
message within 1000ms. Comm Fail Register 0 specifies the local register where the
communications status for this mapping will be stored.
The second mapping reads 8 registers from serial unit D into onboard registers in unit B. Note
that in this case the specified Device ID 6 is the ModBus Address of the serial device D, while
the Server IP Address 192.168.0.200 is the IP Address of unit C since the ModBus TCP to RTU
Gateway at unit C converts the ModBus TCP message to ModBus RTU and routes it out the
serial port to unit D.The third mapping takes the 8 registers read by the second mapping and
writes them to the serial unit A. The specified Device ID 5 is the ModBus Address of the serial
device A, and the Server IP Address 192.168.0.196 is the IP Address of the local unit B since the
local ModBus TCP to RTU Gateway is to route the message out the serial port to unit A.