Plc Device Addressing - ControlByWeb XW-110 User Manual

XW-110™ WiFi Temperature Sensor Users Manual

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
Holding Registers (Read
only)
* 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 Address + PLC Base Address = PLC Address
For example, to read discrete Input 2
Input Address
PLC Base address
PLC Address
Programming the PLC to read from 1002 will return the value of Input 2.
Code Name
Read Holding
Registers
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.
Modbus
Function
03
1
1001
1002
Modbus XW-110 Addresses
Function
03 16 (Battery Voltage)
272-278 (Sensors 1-3)
Modbus/TCP (XW-110-Plus only)
Data Type* PLC Address
Mode 485
32 bits 4001-5000
Data Type PLC Address
32-bit float Addr + 4001
32-bit float Addr + 4001
PLC Address
Mode 584/984
40001-50000
PLC Address
Mode 485 Mode 584/984
Addr + 40001
Addr + 40001
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