Analog Value Processing S5-95F
11.4 Analog Value Representation of Analog Input Modules
Each analog process signal has to be converted into a digital format, to be stored in the process
image input table (PII). The analog signals are converted into a binary digit that is written in two
bytes:
Analog values are represented in two's complement.
Each bit position has a fixed value in powers of two (see Tables 11-2 and 11-5)
The following tables show the analog value representations of the different analog inputs in 2-byte
format. You will need this information to program FB250 and FB251 (see section 11.6).
Table 11-2. Representation of an Analog Input Value as a Bit Pattern
High Byte Low Byte
7 6 5 4 3 2 1 0Bit Number
Analog Value Represent.
7 6 5 4 3 2 1 0
S 2
11
2
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1
2
0
X E OV
Key: S Sign bit 0="+", 1="-"
X Irrelevant bits
E Error bit 0= no wire break; 1=wire break
OV Overflow bit 0= Measured value 4095 units at the most
1= Measured value greater than or equal to 4096 units
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Table 11-3. Analog Input Module 464-8MC11, -8MD11 (Bipolar Fixed-Point Number)
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Units
Measured Value
in V in mA
High Byte Low Byte Range
>4095 20.000 40.0 0 1 1 1 1 1 1 1 1 1111001 Overflow
4095
2049
19.995
10.0048
39.9902
20.0098
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Overrange
2048 10.000 20.0 0 1 0 0 0 0 0 0 0 0000000
1024 5.000 10.0 0 0 1 0 0 0 0 0 0 0000000
1 0.0048 0.0098 0 0 0 0 0 0 0 0 0 0001000
0 0.0 0.0 0 0 0 0 0 0 0 0 0 0000000 Nominal range
-1 -0.0048 -0.0098 1 1 1 1 1 1 1 1 1 1111000
-1024 - 5.000 -10.0 1 1 1 0 0 0 0 0 0 0000000
-2048 -10.000 -20.0 1 1 0 0 0 0 0 0 0 0000000
-2049 -10.0048 -20.0098 1 0 1 1 1 1 1 1 1 1111000 Overrange
-4095 -19.995 - 39.9902 1 0 0 0 0 0 0 0 0 0001000
<-4095 -20.000
-40.0 1000000000001001 Overflow
464-8MC11 (4x±10 V)
464-8MD11 (4x±20 mA)
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11-6
EWA 4NEB 812 6210-02
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