Configuring Modbus Protocol 32-bit Word Order

Background on Modbus Protocol and Big-Endian vs. Little-Endian Word Order

The 1970's Modbus protocol standards give guidance on the protocol, but they don't address the word order beyond the 16-bit register level that was available at that time. For the 16-bit register values, the most significant byte always precedes the least significant byte (this is referred to as Big-Endian word order).

When 32-bit (4 byte) values came about later, the least significant word was mapped onto the lower address of the register pair and was referred to Little-Endian word order). This lack of standardization for values larger than 16 bits has resulted in a situation where Modbus users have to make an arbitrary choice as to which address of the register pair contains the most significant word of a 32-bit value.

Configuring Word Order for groov EPIC

The groov EPIC unit accommodates this variance among Modbus protocols. Follow these steps to configure the word order as Big-Endian or Little-Endian.

I/O to I/O Unit Configuration and Tools

1. From groov Manage Home, select I/O.

2. Select I/O Unit Configuration and Tools.

 

 

 

 

 

 

Configure Modbus Word Order

3. From the I/O Unit menu, select Configuration to access the Modbus 32-bit Float Format setting.

NOTE: The default word order is Big Endian.

Modbus Little Endian

4. In the Modbus 32-bit Float Format, select Big Endian, Word Swapped (Little Endian) to change the word order.

 

Save Temperature Scale 5. Click Save to save the change.

For more information, see the 2267, groov  EPIC User's Guide.

Summary

Summary

How to configure the Modbus word order as Big-Endian or Little-Endian on the groov EPIC unit.