Rockwell Automation 1769-SM2 Compact I/O DSI/Modbus Communication Module - Manual (Page 73)

Understanding Explicit Messaging 5-9
In Multi-Drive mode, any channel can be configured for Modbus RTU
Master operation to communicate with a variety of Rockwell
Automation or 3rd Party RTU Slave devices, such as PowerFlex 7-Class
drives with 20-COMM-H adapters. In the Multi-Drive ladder examples
provided in this manual, CH3 is used to communicate with a PowerFlex
70 drive.
The following Modbus Function Codes are supported:
The format of the Modbus command message data is:
The format of the Modbus response message data is:
The format of the message instruction is different for Modbus RTU
Master operation messaging. For RSLogix 500, format each message as
shown in
Figure 5.7 and see Table 5.D for a description of the data
required in each field. For RSLogix 5000, format each message as shown
in
Figure 5.8 and see Table 5.E .
Modbus RTU Master Operation Messages
Function
Code Name Maximum
Bits/Word Function
Code Name Maximum
Bits/Word
01 Read Coils 512 05 Write Single Coil n/a
02 Read Discrete Inputs 512 06 Write Single Register n/a
03 Read Holding Registers 32 15 Write Multiple Coils 512
04 Read Input Registers 32 16 Write Multiple Registers 512
Word Name Description
1 RTU Slave Address The node address of the Modbus RTU Slave.
2 Function Code The Modbus Function Code to perform.
3 Starting Address The starting coil/register address in the Slave device.
4 Number of bits/words The number of coils/registers to read/write.
5+ Data Words Only used for write messages and contains the data
to be written.
Word Name Description
1+ Data Words Only used for read messages and contains the data
that was read.