XW-110™ WiFi Temperature Sensor Users Manual
Modbus/TCP (XW-110-Plus only)
5.2 PLC Device Addressing
There are generally two schemes for accessing Modbus devices. The first is by specifying the Modbus
function code, memory type, and address. The second, sometimes called PLC addressing, requires only
the address.
Modbus protocol uses four different address ranges for discrete inputs, coils, input registers, and holding
registers. The function code determines the address range of the message. The following are common
function codes and their respective address ranges.
Code Name
Modbus
Function
Data Type*
PLC Address
Mode 485
PLC Address
Mode 584/984
Holding Registers (Read
only)
03
32 bits
4001-5000
40001-50000
* Data types may be implemented at the discretion of the manufacturer. Address ranges may also over
lap. Discrete is a binary or boolean value, 1 or 0.
Function codes, memory types, and addresses can be converted to the PLC addressing equivalent
using the table below. To use the table, look up the row corresponding to the Modbus function code.
Then take the desired XW-110-
Plus
feature address and add to it the address offset in the PLC address
mode column.
Input A PLC Base Address = PLC Address
For example, to read discrete Input 2
Input Address
1
PLC Base address
1001
PLC Address
1002
Programming the PLC to read from 1002 will return the value of Input 2.
Code Name
Modbus
Function
XW-110 Addresses
Data Type PLC Address
Mode 485
PLC Address
Mode 584/984
Read Holding
Registers
03
16 (Battery Voltage)
32-bit float Addr + 4001
Addr + 40001
272-278 (Sensors 1-3)
32-bit float Addr + 4001
Addr + 40001
For 32-bit numbers or floats, two registers must be read starting at the desired address, examples of
each are given for the applicable functions.
Xytronix Research & Design, Inc.
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