Ametek Drexelbrook Impulse GW Series, Installation And Operating Instructions Manual, Page: 70 / 99

Impulse™ Series
64
4.8 Byte Ordering
Data can be accessed as integers (16 bits), long integers (32 bits), and
floating point value (32 bits). The order that the bytes are sent must be
known by the master in order to assembly the bytes into the correct value.
Byte ordering can have a few different terminologies.
1) Big/Little Endian
2) Byte order by number, with 1 indicating the most significant part of
the value, and 4 the least significant,
3) Word/Byte, indicating which word (16 bits, high or low) is sent first,
and which byte of the word (high or low) come first in that byte.
See the following example for accessing a product reading of 46.60 inches.
The integer value will be 4660, which translates to the hex number
0x00001234. The individual bytes, 0x00, 0x00, 0x12, and 0x34 can be
sent the following 4 ways for 32 bits values:
1) Big Endian, Byte order 1234, High Word High Byte (HWHB)
Order sent: 0x00, 0x00, 0x12, 0x34
2) Little Endian, Byte order 4321, Low Word Low Byte (LWLB)
Order sent: 0x34, 0x12, 0x00, 0x00
3) Big Endian Byte Swapped, Byte order 2143, High Word Low Byte (HWLB)
Order sent: 0x00, 0x00, 0x34, 0x12
4) Little Endian Byte Swapped, Byte order 3412, Low Word High Byte (LWHB)
Order sent: 0x12, 0x34, 0x00, 0x00
The individual bytes 0x12, and 0x34 can be sent the following 2 ways for
16 bits values:
1) Big Endian, Byte order 12, High Byte first (HB)
Order sent: 0x12, 0x34
2) Little Endian, Byte order 21, Low Byte first (LB)
Order sent: 0x34, 0x12
4.9 Enron Modbus
Enron Modbus has a few differences from Traditional Modbus. One
difference is the register offsets follow a different numbering scheme,
with integer values residing in the 3XXX range, long integers in the 5XXX
range, and floating points in the 7XXX range. The second difference is
that 32 bits of data can be returned in one register.
The Impulse supports both of these features, by selection of the proper
register value.