Modbus Server Functions and Registers

Modbus Functions

The following Modbus functions are implemented in this version:
  • 01 (0x01) - Read Coils (Output Coils, single bit)
  • 02 (0x02) - Read Discrete Inputs (Descrete Input, single bit)
  • 03 (0x03) - Read Holding Registers (Holding Registers, 16 bit)
  • 04 (0x04) - Read Input Registers (Input Registers, 16 bit)
  • 05 (0x05) - Write Single Coil (Output Coils, single bit)
  • 06 (0x06) - Write Single Register (Holding Registers, 16 bit)
  • 15 (0x0F) - Write Multiple Coils (Output Coils, single bit)
  • 16 (0x10) - Write Multiple Registers (Holding Registers, 16 bit)

Modbus Registers

The Modbus server model provides four data blocks:
  • Discrete Inputs (read only from Modbus, typically Digital Inputs on a PLC)
  • Output Coils (typically Digital Outputs on a PLC)
  • Input Registers (typically Analog Inputs on a PLC)
  • Holding Registers (typically internal registers or Analog Outputs on a PLC)
Each data block contains registers (single or multi bit) which are addressed 0-65535.
When a slave performs any of the above functions, the Modbus Server will automatically add the relevant register address to the display. For read access the initial register value is 0.

Modbus Server Welcome Using Modbus Server