Despite the specification, some Modbus masters may expect "big-endian" word
order (most-significant word first). In such case, you must select "word-swapped"
floating point format in your Modbus master for the Modbus registers of the
device.
A "quiet NaN" value is returned for unavailable values. A quiet NaN is, for example,
7FC00000
hex
; however, the master should understand any NaN value.
A complete 32-bit floating point or integer value should be read and written in a
single Modbus transaction.
A.3.2 16-Bit Integer Format
Some 16-bit integer values in the data registers are scaled to include the necessary decimals.
The scaling factors for those values are shown in the register tables.
Table 12 16-bit Signed Integer Format Details
Value
Description
0000
hex
… 7FFE
hex
Value in range 0 … 32766
8002
hex
… FFFF
hex
Value in range -32766 … -1 (2’s complement)
8000
hex
Value is not available (quiet NaN)
Some values may exceed the signed 16-bit range even in normal operation. To
access such values, use the floating point registers instead.
A.4 Modbus Registers
The decimal numbering of register addresses used in this manual is
1-based (the register addresses start from 1). Note that the register addresses in
actual Modbus messages (Modbus Protocol Data Unit (PDU)) start from zero.
Subtract 1 from the decimal addresses presented in this manual to get the
address used in the Modbus message (for example, the decimal register address
1 becomes register address 0 in the actual Modbus message).
CAUTION!
Accessing unavailable (temporarily missing) measurement data does not generate an
exception. “Unavailable” value (a quiet NaN for floating point data or 0000
hex
for integer
data) is returned instead. An exception is generated only for any access outside the applicable
register ranges.
HPP272 User Guide
M211972EN-B
46