FieldTalk Modbus Slave C++ Library Library version 2.11.0

- Introduction
- Chapters
- Modules
- Classes

Server Functions common to all Modbus 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 |