Beijer Electronics BFI-H2 V1.12 - Manual (Page 63)

User Guide Revision 1.12
63
12. Serial communications
12.1. RS-485 communications
The drive has an RJ45 connector located within the wiring enclosure of the drive. This connector allows the user to set up a drive network via a
wired connection. The connector contains two independent RS485 connections, one for manufacturer proprietary Protocol and one for
Modbus RTU / BACnet. Both connections can be used simultaneously.
The electrical signal arrangement of the RJ45 connector is shown as follows:
Not Used
Not Used
0 Volt
Optibus / Remote Keypad / PC Connection -
Optibus / Remote Keypad / PC Connection +
+24 Volt Remote Keypad Power Supply
RS 485- Modbus RTU / BACnet
RS 485+ Modbus RTU / BACnet
Warning:
This is not an Ethernet connection.
Do not connect directly to an
Ethernet port.
The Optibus data link is used for the Master / Slave function (refer to the Advanced User Guide for further information). Up to 62 slaves can be
connected to one master drive.
The Modbus interface allows connection to a Modbus RTU network as described below.
12.2. Modbus RTU Communications
12.2.1. 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 12.2 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
1
st
Register Address 2 Bytes 1
st
Register Value 2 Bytes
No. Of Registers 2 Bytes 2
nd
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