Siemens SIMATIC ET 200iSP

4 bytes + 1 status byte are required for the representation of a variable in IEEE754 format.
Table 14-33 Variable in IEEE754 format
Byte 7 6 5 4 3 2 1 0 Description
Byte x IEEE variable (IEEE754 format)
Byte x+1
Byte x+2
Byte x+3
Byte x+4 Status byte
HART measured value in IEEE format (byte x to byte x+3)
The following shows the representation of a HART measured value in IEEE format and the
conversion of an IEEE word to a decimal value.
Table 14-34 IEEE754 format (byte x and byte x+1)
Byte x Byte x+1
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Sign 2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
2
-1
2
-2
2
-3
2
-4
2
-5
2
-6
2
-7
Exponent Mantissa
Table 14-35 IEEE754 format (byte x+2 and byte x+3)
Byte x+2 Byte x+3
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
2
-8
2
-9
2
-10
2
-11
2
-12
2
-13
2
-14
2
-15
2
-16
2
-17
2
-18
2
-19
2
-20
2
-21
2
-22
2
-23
Mantissa
Table 14-36 Example: Conversion of IEEE value to decimal value
Byte x Byte x+1 Byte x+2 Byte x+3
0 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Si
gn
Exponent = 2
7
+ 2
0
= 129 Mantissa = 2
-1
+ 2
-2
+ 2
-3
= 0,5 + 0,25 + 0,125 = 0,875
Measured value = (-1)
sign
× 2
(exponent-127)
× (1+mantissa) = (-1)
0
× 2
(129-127)
× (1+0,875) = 1 × 4 × (1,875) = 7,5
Analog electronic modules
14.10 Basics of HART
ET 200iSP
Operating Instructions, 11/2022, A5E00247483-AK 397