Endress+Hauser iTEMP TMT84 - Cyclical Data Exchange

TMT84 Commissioning
Endress+Hauser 31
6.5 Cyclical data exchange
In PROFIBUS
®
PA, cyclical transfer of the analog values to the automation system occurs in data
blocks of 5 bytes. The measured value is represented in the first 4 bytes as floating point numbers
in accordance with the IEEE 754 standard (see IEEE floating point number). The 5th byte contains
status information relating to the measured value, which is implemented as per the profile 3.02
1)
-
specification. The status is shown as a symbol on the device display if available. Refer to chapter 11
"Operation using PROFIBUS
®
PA" for a detailed description of the data types.
6.5.1 IEEE floating point number
Conversion of a hexadecimal value to an IEEE floating point number for measured value acquisition.
The measured values are represented as follows in the IEEE-754 number format and transmitted to
the master class 1:
Formula value = (–1)
VZ
* 2
(Exponent –127)
* (1 + mantissa)
Example:
6.5.2 Block model
The head transmitter supports a maximum of 5 slots for cyclical data exchange. A maximum of 4
values can be selected and transmitted.
Elements of cyclical communication:
1) As per profile 3.01: profile GSD files used or IDENT_NUMBER_SELECTOR set to {0, 129, 130 or 131} or TMT84 GSD file used or
IDENT_NUMBER_SELECTOR set to 1 and "CondensedStatus" parameter to OFF.
As per profile 3.02: TMT84 GSD file used or IDENT_NUMBER_SELECTOR set to 1 and "CondensedStatus" parameter to ON.
If IDENT_NUMBER_SELECTOR = 127, the GSD file used for establishing the cyclical data exchange determines whether diagnosis occurs according to profile
3.01 or profile 3.02.
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
VZ 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
to 2
-23
Exponent Mantissa Mantissa Mantissa
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
Slot Data block Access
1 Analog input 1 Read access
2 Analog input 2 Read access
3 Analog input 3 Read access
4 Analog input 4 Read access
5 Display value Write access