Brand: ABB
Category: Other
Document Type: Manual
Language: EN
Manual for MRP31
Uploaded: April 20, 2026, 8:12 p.m.
Manual Publish Date: 2014-09-01
Warranty Information
None
RS485 Standard
RS-485 is a serial interface standard for communication over a twisted-pair cable, offering better protection against noise and longer transmission distances than RS-232. It is a half-duplex multi-drop network where only one transmitter can be active at a time. The transmission line consists of two wires, A and B, with signal state determined by voltage difference.
The MRP31 Modbus Interface
The MRP31 Modbus communication interface is an optional device for the UMC100.3, enabling connection to an RS-485 network and providing galvanic isolation. It supports Modbus RTU transmission mode and acts as a slave on the network. Through the interface, users can send control commands, read status information and process values, and read device diagnosis information.
Troubleshooting and error codes
| Diagnosis information is locally displayed using LEDs located on the front side of the Modbus interface. | ||
| LED Bus (red, green) | LED DD (red, green) | Meaning |
| Off | Off | Power Supply missing |
| Green flashing | Green flashing | Connection to master missing |
| Red flashing | Red | Bus address of UMC different form the one configured in the master |
| Green | Amber flashing | I/O size mismatch between device and master |
| Green flashing | Parameter mismatch between device and master | |
| Green | Communication lost, supervision timeout time exceeded | |
| Amber flashing | Amber flashing | Initializing |
| Green flashing | Waiting for communication from UMC | |
| Green | OK, normal data exchange | |
| Red flashing | Red flashing | Connection to UMC lost |
| Red | Red | Internal fault. Replace communication interface. |
| Code | Name | Meaning |
| 01 | ILLEGAL FUNCTION | The function code received in the request is not an allowable action for the slave. It could also indicate that the slave is in the wrong state to process a request of this type, for example because it is not configured. |
| 02 | ILLEGAL DATA ADDRESS | The data address received in the request is not an allowable address for the slave. |
| 03 | ILLEGAL DATA VALUE | A value contained in the request data field is not an allowable value for slave. This indicates a fault in the structure of the remainder of a complex request, such as that the implied length is incorrect. |
| 04 | SLAVE DEVICE FAILURE | An unrecoverable error occurred while the slave was attempting to perform the requested action. • Wrong configuration • Not supported baud rate • Serial device connected, but parallel device addressed • Parallel device connected, but serial device addressed • Connected serial device defective |