Yet another Modbus client library for LabVIEW.
LabVIEW 2015 and higher.
- RTU, ASCII and TCP protocols via serial or network connection.
- Implemented read/write functions (Modbus function codes):
- Read Coils / Discrete Inputs / Holding Registers / Input Registers (1/2/3/4)
- Write Single Coil / Holding Register (5/6)
- Write Multiple Coils / Holding Registers (15/16)
- Splitting single read/write requests into multiple requests with valid number of memory elements.
- Automatic reconnection to device.
- Support of multiple devices on the same serial port (VISA Lock/Unlock).
- Possibility of other Modbus function code (including user-defined) implementation.
Modbus Serial Line Protocol and Implementation Guide states that:
- 8 data bits should be used for Modbus RTU and 7 data bits - for Modbus ASCII.
- 1 stop bit should be used if there is parity bit and 2 stop bits - if there is no parity bit.
However there is a number of devices that do not follow these rules. So Initialize Serial.vi allows to set the same parameters as basic VISA Configure Serial Port.vi. Limitations on serial parameters can be implemented in higher level specific device library.
All implemented Read/Write VIs internally use Command.vi with function code and data in as inputs and data out as output.
For Modbus TCP and Modbus ASCII this VI can be used with any function code, since these protocols allow to receive responce data without knowing its size beforehand. For Modbus RTU descendant class should be created with overriden Read RTU Data.vi.
Simple Modbus client application.
Tests client-server connection and measures transaction rate.
Tests Modbus server by writing to random memory locations, reading back and comparing data.
Modbus (Wikipedia)
Modbus Protocol Specification
Modbus Serial Line Protocol and Implementation Guide