Modbus Communication API

When using the RTU protocol, the Assurance Monitoring System will answer to a master query only if the query contains the same slave address as defined on the Assurance device. The permitted addresses range from 1 to 254 (0x01 to 0xFE), and there should be no controllers with the same address on the same line.

* During normal operation, the Modbus Master transmits Modbus RTU requests and automatically appends the required CRC-16 checksum to each message. The Assurance system receives incoming messages and verifies the accuracy of the CRC-16 checksum. If the CRC is found to be incorrect—whether due to electrical noise, timing discrepancies, or malformed messages—the Assurance system will disregard the request. In such cases, the Modbus Master will report a communication fault. This may be indicated as a timeout, absence of response, or an explicit error notification within the user interface. It is recommended to configure the Modbus Master to provide alerts or notifications if a communication fault with the Assurance system is detected, enabling prompt troubleshooting and system reliability.

The Modbus settings on the Assurance Monitoring System can be configured using a serial console, such as PuTTY. The Assurance System can be connected to a laptop with the serial console software using the DB9 serial port located on the backside of the Assurance faceplate. This connection requires a standard straight-through serial cable (non null-modem). The baud rate for the DB9 port is 115200.

Below is a list of commands that may be useful in configuring the Assurance System.

The Assurance Monitoring System features a block of DIP switches (SW1) to set the desired termination resistance for Modbus RS485 communication. SW1 is located on the back side of the Assurance faceplate assembly adjacent to the Modbus RS485 termination points. The below table outlines the available termination resistor settings with corresponding DIP switch configurations.