Beijer Electronics BFI-P2 V1.21 - Manual (Page 46)

User Guide Revision 1.12
www.beijerelectronics.com
46
9. Serial communications
9.1. RS‐485 communications
An RJ45 connector located on the drive allows the user to connect the drive to a Modbus RTU network or CANBus via a wired connection.
The electrical signal arrangement of the RJ45 connector is shown as follows:
CAN‐
CAN+
0 Volt
Remote Keypad / PC Connection ‐
Remote Keypad / PC Connection +
+24 Volt Remote Keypad Power Supply
RS 485‐ Modbus RTU
RS 485+ Modbus RTU
9.2. Modbus RTU Communications
9.2.1. 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
detail in section 9.2.2 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 Function Code (03) 1 Byte
1
st
Register Address 2 Bytes Byte Count 1 Byte
No. Of Registers 2 Bytes 1
st
Register Value 2 Bytes
CRC Checksum 2 Bytes 2 nd Register Value 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