Modbus RTU Specification
Modbus RTU - Overview
Modbus RTU communication can be used to control and monitor the drive.
The following table details the Modbus Specification that is supported by the Elevator Core.
Protocol | Modbus RTU |
|---|---|
Baud Rate | 9600bps, 19200bps, 38400bps, 57600bps, 115200bps (default) |
Parity | Even, Odd, or None |
Stop Bits | 1 bit (2 bits for no parity) |
Optional Modules | None - Built in as Standard |
Physical Signal | RS 485 (2-wire) |
User interface | RJ45 |
Supported Function Codes | 03 Read Holding Registers 06 Write Single Register 16 Write Multiple Registers |
Communication Loss Actions | Trip (default) Ramp to stop then trip Ramp to stop only (No trip) Run at Inspection Speed (P8-08) |
Maximum Number of drives on network | 247 |
What can you do with Modbus RTU
The following features are available with Modbus and the table below briefly explains how to use them. For a full explanation see the topics linked.
Feature | How to use | Topic Links |
|---|---|---|
Change Parameters | Write to Parameter Registers | |
Read Parameters | Read with Parameter Registers | |
Start and Stop the Drive | Use the Control Word to start and stop the drive | |
Reset Faults | Use the Control Word to reset drive faults | |
Set the Drive Speed | Use the Speed Reference Register to control the drive speed | |
Fault & Status Monitoring | Monitor the Drive status and any fault code |
Modbus Telegram Structure
The drive supports Master / Slave Modbus RTU communications, using the 03 Read Holding Registers and 06 Write Single Holding Register commands. Many Master devices treat the first Register address as Register 0; therefore, it may be necessary to convert the Register Numbers detailed by subtracting 1 to obtain the correct Register address.
The telegram structure is as follows:-
Command 03 – Read Holding Registers | ||||||
|---|---|---|---|---|---|---|
Master Telegram | Length | Slave Response | Length | |||
Slave Address | 1 | Byte | Slave Address | 1 | Byte | |
Function Code (03) | 1 | Byte | Starting Address | 1 | Byte | |
1st Register Address | 2 | Bytes | 1st Register Value | 2 | Bytes | |
No. Of Registers | 2 | Bytes | 2nd Register Value | 2 | Bytes | |
CRC Checksum | 2 | Bytes | Etc... | |||
CRC Checksum | 2 | Bytes | ||||
Command 06 – Write Single Holding Register | ||||||
Master Telegram | Length | Slave Response | Length | |||
Slave Address | 1 | Byte | Slave Address | 1 | Byte | |
Function Code (06) | 1 | Byte | Function Code (06) | 1 | Byte | |
Register Address | 2 | Bytes | Register Address | 2 | Bytes | |
Value | 2 | Bytes | Register Value | 2 | Bytes | |
CRC Checksum | 2 | Bytes | CRC Checksum | 2 | Bytes |