Pepperl+Fuchs WHA-GW Manual page 86

WHA-GW-*
Operation
Bit
0x20
0x10
0x08
0x04
0x02
0x01
Dynamic variable mapping format
For each HART device, the 5 possible CMD 3 floating-point dynamic variables are
sequentially mapped (the CMD 3 units code values are not mapped). If a device does not
support a specific dynamic value, a "NaN" (Not a Number) floating-point value is returned
(namely, 0x7F, 0xA0, 0x00, 0x00).
The CMD 3 dynamic variables follow the IEEE-754 (IEC 559) single-precision floating-point
format (see following table).
Sign of the Fraction
The same format is also used for the Modbus 32-bit floating point values.
The Modbus protocol does not explicitly specify any 32-bit data element. However, the
usage of 2 consecutive 16-bit registers is the de-facto standard way to map a single-
precision IEEE-754 floating-point value. Note that the Modbus floating value will be
transmitted in the "big-endian" style. For example, the number 123456.00 as defined in the
IEEE-754 standard appears as follows:
Byte 0
0x00
This number will be transmitted from the Gateway to the Modbus master in the following
sequence:
47 F1 20 00
where "00" – the less significant byte – is the first one to be transmitted.
86
Parameter Description
Cold start A power failure or device reset has
occurred.
More status More status information is available via
available Command 48 "Read additional status
information".
Loop current fixed The loop current is being held at a fixed
value and is not responding to process
variations.
Loop current The loop current has reached its upper (or
saturated lower) endpoint limit and cannot increase
(or decrease) any further.
Non-primary A device variable not mapped to the PV is
variable out of limits beyond its operating limits.
Primary variable out The PV is beyond its operating limits.
of limits
8-bit Exponent
Byte 1 Byte 2
0x20 0xF1
23-bit Fraction
Byte 3
0x47