Modbus/Tcp & Modbus Rtu Function Codes; Function Code Definitions; Table 4-1 Modbus/Tcp And Modbus Rtu Function Codes Definitions - Honeywell HC900 User Manual

4. Modbus/TCP & Modbus RTU Function Codes

4.1 Function code definitions

The HC900 Modbus protocol uses a subset of the standard Modbus function codes to provide access to process-
related information. These standard function codes provide basic support for IEEE 32-bit floating point numbers, 32-
bit unsigned/signed integer and 16-bit integer register representation of instrument's process data.
Repolling of data is not supported by this instrument.

Table 4-1 Modbus/TCP and Modbus RTU Function Codes Definitions

Function Code
01 Read Coil Status
02 Read Input Status
03 Read Holding Registers
04 Read Input Registers
05 Force Single Coil
06 Preset Single Register
08 Loopback Test
16 (10h) Preset Multiple Registers
17 (11h) Report Device ID
Revision 13
April 2017
Name
Read the state of a digital output
Read the state of a digital input
Read data in 16-bit Register Format (high/low). Used to read
integer or floating point process data. Registers are
consecutive and are imaged from the instrument to the host.
Provides Read access to any Analog Input Channel
positioned in any Rack or Slot.
Write data to force a digital output ON/OFF
Values of FF 00 forces digital output ON
Values of 00 00 forces digital output OFF
Values of FF FF releases the force of the digital output
All other values are illegal and will not effect the digital output.
Write Data in 16-bit Integer Format (high/low) ONLY.
Used for diagnostic testing of the communications port.
Write Data in 16-bit Format (high/low). Used to write integer
and floating point override data. Registers are consecutive
and are imaged from the host to the instrument.
Read instrument ID and connection information, ROM
version, etc.
HC900 Process Controller Communications User Guide
Modbus/TCP & Modbus RTU Function Codes
Function code definitions
Usage
17