Serial Port Monitor - Software Serial Port sniffer, logger & protocol analyzer for Windows


MODBUS is an application layer messaging protocol, positioned at level 7 of the OSI model that provides client/server communication between devices connected on different types of buses or networks.

The industry’s serial de facto standard since 1979, MODBUS continues to enable millions of automation devices to communicate. Today, support for the simple and elegant structure of MODBUS continues to grow. The Internet community can access MODBUS at a reserved system port 502 on the TCP/IP stack.

The Modbus protocol has two different types of interaction: ASCII/RTU. In ASCII mode data is wrapped into the packet and transmitted as an ASCII string. The first byte of packet is used for identification – its value should be equal to 0x3A. Packet ends with two special bytes - 0x0D and 0x0A.

MODBUS View visualizer is compliant with MODBUS APPLICATION PROTOCOL SPECIFICATION V1.1a. There are several different implementations of Modbus Protocol. Different companies implement and document their own specific extensions to Modbus Protocol. Function and command names could vary: for example, Preset Single Register command in one implementation equals to Write Single Register command in the standard.

MODBUS View visualizer parses MODBUS protocol requests and responses, while the MODBUS Send Module can be used to construct and send MODBUS requests and responses. The visualizer is part of the monitoring infrastructure, which you can use it to monitor the existing connection between the application and a serial device. The MODBUS Send Module, on the other hand, allows you to control the MODBUS-compliant device without the need of any third party controlling application. In this case, the MODBUS View visualizer, if configured, can be used to see the requests sent by the MODBUS Send Module and packets the device responds with.

You can set the filtering on Tools » Settings, Filtering Tab page.

The following settings govern the behavior of the visualizer (they all are controlled from the Tools » Settings, General Tab):

MODBUS View visualizer supports Generic Filtering platform.