Modbus Rtu Communications; Introduction; Modbus Rtu Specification; Rj45 Connector Configuration - ABB ACS255 User Manual

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11. Modbus RTU Communications

11.1. Introduction

The ACS255 can be connected to a Modbus RTU network via the RJ45 connector on the front of the drive.

11.2. Modbus RTU Specification

Protocol
Error check
Baud rate
Data format
Physical signal
User interface

11.3. RJ45 Connector Configuration

Connection details are shown on page 24.

11.4. 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 detail in section 45 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 Byte
Function Code (03) 1 Byte
1 st Register Address 2 Bytes
No. Of Registers 2 Bytes
CRC Checksum 2 Bytes

11.5. Modbus Register Map

Par.
Register
Type
Number Commands
1 - R/W
2 - R/W
4 - R/W
6 - R
7 R
8 R
11 - R
20 0120 R
21 0121 R
22 0111 R
23 0107 R
24 0110 R
All user configurable parameters are accessible as Holding Registers, and can be Read from or Written to using the appropriate Modbus
command. To access drive parameters refer to section 11.6 for parameter register map.
Depending on the operating mode of the drive – some parameters cannot be changed whilst the drive is enabled for example.
Modbus RTU supports sixteen bit integer values, hence where a decimal point is used in the drive parameter; the register value will be
multiplied by a factor of ten, E.g. Read Value of parameter 2008 MAXIMUM FREQUENCY / SPEED LIMIT = 500, therefore this is 50.0Hz
Modbus RTU
CRC
9600bps, 19200bps, 38400bps, 57600bps, 115200bps (default)
1 start bit, 8 data bits, 1 stop bits, no parity.
RS 485 (2-wire)
RJ45 (see page 24 for more information)
Slave Response Length
Slave Address 1
Starting Address 1
1 st Register Value 2
nd
2 Register Value 2
Etc...
CRC Checksum 2
Function
Supported
Low Byte
03,06 Drive Control Command
03,06 Modbus Speed reference setpoint
03,06 Acceleration and Deceleration Time
03 Error code
03 Output Motor Frequency
03 Output Motor Current
03 Digital input status
03 Analog Input 1 value
03 Analog Input 2 value
03 Speed Reference Value
03 DC bus voltage
03 Drive temperature
Command 06 – Write Single Holding Register
Master Telegram
Byte Slave Address
Byte Function Code (06)
Bytes Register Address
Bytes Value
CRC Checksum
Bytes
Range Explanation
High Byte
0..3 16 Bit Word.
Bit 0 : Low = Stop, High = Run Enable
Bit 1 : Low = Decel Ramp 1 (parameter 2203),
High = Decel Ramp 2 (Parameter 2206)
Bit 2 : Low = No Function, High = Fault Reset
Bit 3 : Low – No Function, High = Coast Stop
request
0..5000 Setpoint frequency x10, e.g. 100 = 10.0Hz
0..60000 Ramp time in seconds x 100, e.g. 255 = 2.5 seconds
Drive status Low Byte = Drive Error Code, see page 50
High Byte = Drive Status as follows :-
0 : Drive Stopped,
0..20000 Output frequency in Hz x10, e.g. 100 = 10.0Hz
0..480 Output Motor Current in Amps x10, e.g. 10 = 1.0 Amps
0..15 Indicates the status of the 4 digital inputs
Lowest Bit = 1 Input 1
0..1000 Analog input % of full scale x10, e.g. 1000 = 100%
0..1000 Analog input % of full scale x10, e.g. 1000 = 100%
0..1000 Displays the setpoint frequency x10, e.g. 100 = 10.0Hz
0..1000 DC Bus Voltage in Volts
0..100 Drive heatsink temperature in ºC
Length Slave Response
1 Byte Slave Address
1 Byte Function Code (06)
2 Bytes Register Address
2 Bytes Register Value
2 Bytes CRC Checksum
1: Drive Running, 2: Drive Tripped
Length
1 Byte
1 Byte
2 Bytes
2 Bytes
2 Bytes