Honeywell HC900 User Manual page 22

Modbus Double Register Format
Unsigned/signed 32-bit Register Formats
FP BB – Big Endian Byte Swapped Format
The value 12345678 Hex will be represented as follows:
Bit 23 Bit 16 Bit 31 Bit 24 Bit 7 Bit 0 Bit 15 Bit 8
Byte 3 Byte 4 Byte 1 Byte 2
34 Hex 12 Hex 78 Hex 56 Hex
Low High Low
High
REGISTER N REGISTER N+1
(High) (Low)
14 HC900 Process Controller Communications User Guide Revision 13
April 2017