User manual

Weidmuller Wireless Ethernet Modem & Device Server WI-MOD-E-G/A User Manual

Rev.2.16 www.weidmuller.com  47

An example of the Modbus functionality of the WI-MOD-E is illustrated here. In this example the status of the onboard

digital input at C will be reflected at the onboard digital output at B. Also, 8 single bit registers from Modbus serial device D

will be transferred to A.

Figure 37 - Modbus Mappings

Unit B is configured with Modbus TCP Server enabled and Device ID = 1, Unit C is configured as shown above.

 The first will write the register 4300 (Local Digital Input) to server IP address 192.168.0.200 (Unit B), Device ID

#1, register 4320 (Local Digital output).

 The second mapping shows a Modbus read command of 8 Discretes starting at register 1 (Destination Reg) on

Device ID #6 connected to IP address 192.168.0.123 (it self) and store the values at register #1 locally.

 The third mapping shows the Modbus write command (Write Coils) which is writing the local 8 I/O’s starting at

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 the registers at unit B will be reset if a successful Modbus transaction involving that

section 3.12 - “RS-232 / RS485 Modbus TCP/RTU Converter”) 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 Discrete

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.

Since the WI-MOD-E supports Modbus TCP Client and Server simultaneously, the Modbus TCP Server for unit B above

could also be enabled. This would allow one (or more) external Modbus TCP Clients anywhere on the extended wired or

wireless network to connect to unit B and monitor the status of the I/O registers – including the I/O at units A, C, and D.

This is a very powerful and flexible feature which could, for example, be exploited by a central monitoring facility or

SCADA.