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Cooper Bussmann 915U-2 Wireless Mesh I/O and Gateway User Manual
Rev Version 1.2.2
Figure 61 Modbus TCP Client Mapping
Local Register
(Master)
When the Function Code Modbus command is “Read” the Local Register field will
be the destination register (output location) on the local device. When the Function
Code command is “Write” the Local Register field will be the originating register
(input location) on the local device.
I/O Count
The number of consecutive I/O values in the mapping.
Function Code
(Command Type)
The Function Code Modbus command determines if the command will be “Read” or
“Write” and what type of register will be used. When entering a mapping, you need
to select “Read” or “Write” from the drop-down list in the Command Type field, and
then select one of the four radio buttons representing the register types. Selecting the
register type will change the Destination (slave) register address range to a suitable
range.
Destination Register
(Slave)
The register location on the TCP server/RTU slave device. The register selection
offered will be appropriate for the Modbus command selected in the Command field.
Device ID
The unit address (device ID) of the Modbus TCP server or Modbus RTU slave.
Server IP Address
Network Address
(TCP client only.) The IP address of the Modbus TCP server.
Server Port (TCP
Client only)
The server port of the slave device, Modbus TCP will usually be the standard port
address of 502.
Serial Port (Modbus
RTU only)
This is the serial port used to connect to the device. Select the port from the
drop-down list.
Response Time
The amount of time the TCP client or Modbus master waits for a response from a
TCP server or an RTU slave device before registering a Communications Fail.
Fail Reg
The Comms Fail indication register can be a physical output, such as DIO #1–8 (Reg
1-8), which will turn on a digital output when in fail. It can also be configured as an
internal holding register (Reg 30501), which will show the fail indication as well as
any Modbus error codes. This is useful for diagnosing communication problems. For
Modbus error code descriptions, see Appendix D.
Modbus TCP Mapping Examples
In the example in Figure 62, the first mapping (#1) shows the Modbus client (master) is configured to read analog
values from a device connected on the LAN. The mappings function code is “Read” and is reading a count of four
values (analogs) from the Ethernet address 192,168.0.17, device ID #10, starting at address 30001, and then writing
