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.
1. From groov Manage Home, select I/O.
2. Select I/O Unit Configuration and Tools.
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.
4. In the Modbus 32-bit Float Format, select Big Endian, Word Swapped (Little Endian) to change the word order.
|5. Click Save to save the change.|
For more information, see the 2267, groov EPIC User's Guide.