Serial Communications; Rj45 Connector Pin Assignment; Modbus Rtu Communications - ABB ACS255 User Manual

10. Serial communications

10.1. RJ45 Connector Pin Assignment

ACS255 has an RJ45 connector on the front of the control panel. This connector allows the user to set up a drive network via a wired connection.
The connector contains multiple interfaces for different communication protocols.

PC and peripheral connection only

Modbus RTU

CANBus
The Remote keypad connection is always available, and can be used simultaneously with other interfaces, however only one other interface may
be used, e.g. If Modbus RTU is in use, CAN is disabled.
The electrical signal arrangement of the RJ45 connector is shown as follows:

10.2. Modbus RTU Communications

10.2.1. Modbus Telegram Structure
The ACS255 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 in section 10.2.4 by subtracting 1 to obtain the correct Register address. The telegram structure is as follows.
Command 03 – Read Holding Registers
Master Telegram Length
Slave Address 1
Function Code (03) 1
1 st Register Address 2
No. Of Registers 2
CRC Checksum 2
Command 06 – Write Single Holding Register
Master Telegram Length
Slave Address 1
Function Code (06) 1
Register Address 2
Value 2
CRC Checksum 2
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
Slave Response
Byte Slave Address
Byte Function Code (03)
Bytes Byte Count
Bytes 1 st Register Value
Bytes 2 nd Register Value
Etc...
CRC Checksum
Slave Response
Byte Slave Address
Byte Function Code (06)
Bytes Register Address
Bytes Register Value
Bytes CRC Checksum
Length
1 Byte
1 Byte
1 Byte
2 Bytes
2 Bytes
2 Bytes
Length
1 Byte
1 Byte
2 Bytes
2 Bytes
2 Bytes
55