Endress+Hauser PROFIBUS-DP, Руководство по эксплуатации, Страница: 21 / 52

SmarTec S CLD 132 PROFIBUS-PA/-DP Operation
Hauser 21
IEEE-754 floating point number:
Explanation of measuring range switch (MRS)
Customising the cyclic data telegram
You can customise the cyclic telegram to better meet the requirements of a process.
The tables above represent the maximum contents of the cyclic data telegram.
If you do not want to use all the output variables of the transmitter, you can use the
device configuration (CHK_CFG) to eliminate individual data blocks from the cyclic
telegram via the PLC software. Shortening the telegram improves the data throughput
rate of a PROFIBUS system. You should only keep those blocks active which you
process further in the system. You can do this by means of a ”negative” selection in the
configuration tool.
To achieve the correct structure of the cyclic data telegram, the PROFIBUS master must
send the identification FREE_PLACE (00h) for the non-active blocks.
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
Sig
n 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
−17
2
−18
2
−19
2
−20
2
−21
2
−22
2
−23
Exponent Mantissa Mantissa Mantissa
Formula: Valu
e = (-1)
sign
* 2
(exponent - 127)
* (1 + mantissa)
Example: 40 F0 00 00 h = 0100 0000 1111 0000 0000 0000 0000 0000 b
Valu
e
= (-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
MRS Function
reser
ved
reser
ved
reser
ved
reser
ved
reser
ved
E2 E1
Deci
mal
H
e
xad
eci
mal
Number of binary inputs = 2; E1 and E2 active
- - - - - 0 0 0 0x00 MRS 1
- - - - - 0 1 1 0x01 MRS 2
- - - - - 1 0 2 0x02 MRS 3
- - - - - 1 1 3 0x03 MRS 4
Number of binary inputs = 1; E1 and E2 active
- - - - - 0 0 0 0x00 MRS 1
- - - - - - 1 1 0x01 Hold on
- - - - - 1 0 2 0x02 MRS 2
Number of binary inputs = 0; E1 active
- - - - - - 0 0 0x00 Hold off
- - - - - 1 1 0x01 Hold on