Endress+Hauser Promag 53 - Cyclic Data Exchange

Promag 53 PROFIBUS-DP/-PA 6 Commissioning
Endress+Hauser 93
6.4.1 Cyclic data exchange
In the case of PROFIBUS-DP/-PA, the cyclic transmission of analog values to the auto-
mation control system is effected in data blocks of 5 bytes. The measured value is por-
trayed in the first 4 bytes in the form of flowing point numbers in accordance with
IEEE 754 standard (see IEEE floating point number). The 5th byte contains status infor-
mation pertaining to the measured value which is implemented in accordance with the
Profile 3.0 specifications (see Page 90). The status will be indicated on the display of
the device (see Page 65).

Note:
A detailed description of the data types can be found in the Slot/Index lists in the sepa-
rate “Description of Device Functions” manual.
IEEE floating point number
Conversion of a hexadecimal value into an IEEE floating point number for measured
value detection.
The measured values are shown in numerical format IEEE-754 in the following manner
and are transferred to Class 1 master:
Formula value = (-1)
Sign
* 2
(exponent -127)
* (1 + Mantisse)
Example: 40 F0 00 00 hex = 0100 0000 1111 0000 0000 0000 0000 0000 binary
Value = (-1)
0
* 2
(129-127)
* (1 + 2
-1
+ 2
-2
+ 2
-3
)
= 1 * 2
2
* (1 + 0.5 + 0.25 + 0.125)
= 1 * 4 * 1.875 = 7.5
Byte n Byte n+1 Byte n+2 Byte n+3
Bit 7
Bit 6 Bit 0 Bit 7 Bit 6 Bit 0 Bit 7 Bit 0 Bit 7 Bit 0
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
2
-8
2
-9
2
-10
2
-11
2
-12
2
-13
2
-14
2
-15
2
-16
...2
-23
Exponents Mantisse Mantisse Mantisse