Modbus decoder troubleshoots PLC applications

Posted By : Mick Elliott
Modbus decoder troubleshoots PLC applications

The analysis capabilities of Pico Technology’s PicoScope have been enhanced with the addition of Modbus ASCII and Modbus RTU decoders. Capable of analysing Modbus (RS-232/RS-485) signals, it becomes a tool for troubleshooting industrial PLC applications – from installation and commissioning to maintenance and repair operations.

The PicoScope USB-connected PC oscilloscope offers  six test and measurement instruments in one – including protocol analysis, logic and spectrum analysers and a signal/arbitrary waveform generator. This capability makes PicoScope outstanding for signal integrity measurements on serial buses. The Modbus decoder is available for all PicoScope models, from the low-cost 2000 Series through to the top-of-the-range 6000 Series.

For sources that are not referenced to earth, such as RS-485, the recently introduced PicoScope 4444 Series permits quick and easy differential measurements on up to four channels without the expensive external active differential probes typically needed in industrial applications.

PicoScope includes a comprehensive set of automated and ruler-based on-screen measurements as standard.

The PicoScope decoder supports master and slave devices, standard and custom baud rates, and one or two ID bytes.

Hundreds or thousands of Modbus messages can be captured with each acquisition using the deep memory provided in most PicoScope models. Each message is stored with start/end timing information, device IDs, function codes, transmitted data and CRC information as well as data validity checks.

The table of acquired messages can be analysed directly within the iscilloscope or can be exported in CSV format for offline analysis.

A link file helps to speed analysis by cross-referencing hexadecimal field values, such as the slave ID, to plain text.

Clicking on a decoded packet takes you to the corresponding point on the analog waveform, making it easy to troubleshoot bus errors.

Modbus decoding and analysis is included as standard in the latest PicoScope beta version 6.13, which now supports a total of 18 serial protocols.


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