This document describes how to configure a 1769-SM2 module to communicate with Modbus RTU slave devices over an RS485 network. It explains how to set the configuration mode switch and configuration data table to define the communication parameters for up to 31 slave devices per channel. Logic is provided for reading holding register data from the slave devices using function codes, register addresses, and data lengths specific to each device. Notes are included on checking slave status and parameters using third-party software. References for the module manual and RS485 connector pinout are also listed.

1. By: Anish Shrivastava

2. AK-U0-RJ45-TB2P
1769-L35E-CompactLogix5335E (RJ45 – RS485 Splitter)
Controller
1769-SM2-
Module
Modbus Slaves Modbus Cable
Modbus RTU Network
PCS Controller SIPROTEC 4 7SJ61
Conzerv EM6400
PPI-402 Multifunction Protection
Relay

3. Setting the Configuration Mode Switch in 1769 SM2 Module
Before installing the module, make sure its Configuration Mode Switch is correctly set.
SW1 Setting Description SW2 Setting
CONT (Controller) Default setting—The 1769-SM2 module uses the configuration
Single Position (For Single drive per
back position data downloaded from the controller on power-up and when the
channel)
controller is placed in run mode.
Multi-Drive Position (For Max 5
PARAM (Parameter) The 1769-SM2 module uses its internal parameter settings to
drives per channel or up 31 RTU
front position configure the module.
slave devices per channel)
Select SW1 in Controller Position and SW2 in Multi-Drive Position.

4. Module Configuration
In Logic
Configuration and Logic

5. Module Configuration
In Logic
Configuration and Logic

6. 1769-SM2 Module
Configuration Data
Configuration and Logic

7. 1769-SM2 Module
Configuration Data Table
Configuration and Logic

8. Configuration and Logic
Use these data values to configure the configuration data table of SM2 module.
For DSI I/O Config Select “5” for modbus RTU slave.
RTU Baud Rate Configuration RTU Format Configuration
Where The RTU format
consists of three
components: data bits (8 data
bits only), parity
(None, Even or Odd), and stop
bits (1 or 2).
e.g.: For None parity and 2 stop bits select value “3”.
e.g.: For baud rate 9600 bits/sec select value “2”.
For RTU Rx Delay, RTU Tx Delay And RTU MSG Timeout select the values according to
the load in controller and scan time of controller in such a way that the slave device
has sufficient time to respond to the master.

9. Logic for reading
Holding Register data of RTU Devices Configuration and Logic

10. Logic for reading
Holding Register data of RTU Devices Configuration and Logic

11. Configuration and Logic
Holding Register data of RTU Devices
Logic for reading
Path Format: Module Name, 2, Channel
No.

12. Logic for reading
Holding Register data of RTU Devices Configuration and Logic
Refer to Notes

13. Notes
Slave Device ID: Can be configure for each slave device. (0-255)
Function Code: Can be differ according to the register type.(Such as 3-Holding Register, 4-Input Register)
To See Example
Register Address and Length: May vary according to the slave device’s parameters.
Click Here
( For PCS Controller: Register Address is “3” and its data length is “1”.)
Please select the proper data mentioned above for slave devices otherwise communication fails.
For detailed information about these parameters please refer to the user manual of the particular slave
device.
To check slave communication status and device parameters: use ModScan32 (3rd party software) if
available.
AK-U0-RJ45-TB2P (RJ45 – RS485 Connector) Pin Out:

14. References
1769 SM 2 Module User Manual
http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1769-um013_-en-p.pdf

15. THE
END