Applies To:
  • CitectSCADA 5.10

The way in which Citect combines two PLC registers to form a "long" data type has been extended to support big endian addressing. This enhancement is effective for all of the MODBUS family of drivers - MODBUS, MODBUSA, MODCELL, MOORE and MBPLUS.  

When using the MODBUS protocol, Citect will combine two registers to store a long data type in a PLC. The way in which it does this is set by the "LongDataType" parameter in the "citect.ini" file. Initially, the two options (both little endian) were as follows:

LongDataType = 0 (the default) implies 10,000 * low register + high register
LongDataType = 1 implies 65,536 * low register + high register

These have been extended to include two new formats which use big endian addressing, i.e.

LongDataType = 2 implies 10,000 * high register + low register
LongDataType = 3 implies 65,536 * high register + low register