We are pleased to announce that the latest Modbus protocol supporting version of the NG firmware, V1.19, used in the current Gascard, Chillcard and Guardian products is now available.

This new version supports communication over the RS232 interface using industry standard Modbus RTU commands. When combined with an RS232 to RS485 converter and a “silent” version of the bootloader it allows Modbus RTU communication with several NG units over an RS485 bus. This modification allows for simpler and longer range digital communications in systems that use distributed sensors or systems that employ multiple sensors (different ranges or gases or types) in a single installation. 

Modbus RTU Overview

The Modbus RTU -communication protocol is based on the master-slave architecture. It uses RS-485, RS-422, RS-232 interfaces to communicate between master and slave.

Modbus RTU messages sent from the master controller consist of the address of the SlaveID device, a function code, data, depending on the function code and finally the CRC of the checksum.

This allows a master station to interrogate a single slave over an RS232 link or, when combined with an RS-485 interface, multiple units to be interrogated on a single bus in sequence.

Modbus RTU is widely used in Supervisory Control and Data Acquisition (SCADA) systems where polling rates are relatively low (~ one sample per slave per second).

The Modbus version of the Gascard NG firmware supports the reading of the Gascard’s key output’s:- concentration, range, pressure and unit serial number. It also supports the zero and span calibration commands.

Changing to and from the standard Gascard NG RS232 protocol is accomplished using an on-board bit switch (4) and a unit restart. New commands have been added to the standard Gascard NG protocol to enable the setting up of the Modbus RTU communications mode: – baud rate, slave address, parity etc.

For further information or enquiries regarding the Modbus RTU, simply contact our sales team who will be happy to help.