Server Functions common to all Protocol Flavours |
The FieldTalk Modbus Slave Protocol Library's server engine implements the most commonly used Modbus data functions as well as some control functions. The functions to perform PLC program download and other device specific functions are outside the scope of this library.
All Bit Access and 16 Bits Access Modbus Function Codes have been implemented. In addition the most frequently used Diagnostics Function Codes have been implemented.
The following table lists the functions supported by the slave:
Function Code | Current Terminology | Classic Terminology |
|---|---|---|
Bit Access | ||
1 | Read Coils | Read Coil Status |
2 | Read Discrete Inputs | Read Input Status |
5 | Write Single Coil | Force Single Coil |
15 (0F hex) | Write Multiple Coils | Force Multiple Coils |
16 Bits Access | ||
3 | Read Multiple Registers | Read Holding Registers |
4 | Read Input Registers | Read Input Registers |
6 | Write Single Register | Preset Single Register |
16 (10 Hex) | Write Multiple Registers | Preset Multiple Registers |
22 (16 hex) | Mask Write Register | Mask Write 4X Register |
23 (17 hex) | Read/Write Multiple Registers | Read/Write 4X Registers |
Record Access | ||
20 (14 hex) | Read File Record | Read General Reference |
21 (15 hex) | Write File Record | Write General Reference |
Diagnostics | ||
7 | Read Exception Status | Read Exception Status |
17 (11 hex) | Report Slave ID | Report Slave ID |
43 (2B hex) subcode 14 (0E hex) | Read Device Identification |