Issue
Debugging RPC Modbus RTU
Product Line
EcoStruxure Building Operation
Environment
- SmartX IP RP series
- RP-C Modbus
Cause
The RPC has no transmit and receive LEDs for the Modbus and no packet data can be logged or viewed. In the Technical Reference Guide, a search for "SmartX IP Controller - RP Series Modbus" provides information on the differences between the Automation Server and RPC Modbus operations.
Resolution
There are a couple of options, but they involve using another device connected to the Modbus network to view the packets
- Use a PC based Modbus slave simulator
- Use an Automation Server set up as a Modbus RTU slave, the packets can be sent to the trace log then viewed in the usual way.
Note: A defect with v3.2.1 EBO means this solution cannot be used to monitor a Modbus RTU bus because the AS replies to all requests and may cause conflicts on the network. All versions 3.1.2 and earlier work fine, as well the EBO 2022 (v4.0.1) as detailed in the Known Issue Modbus Slave incorrect response
