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Analog Value Processing
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
Bit Number
Analog Value Represent.
Key:
S
X
E
OV
Table 11-3. Analog Input Module 464-8MC11, -8MD11 (Bipolar Fixed-Point Number)
Measured Value
Units
in V
>4095
20.000
4095
19.995
2049
10.0048
2048
10.000
1024
5.000
1
0.0048
0
0.0
-1
-0.0048
-1024
- 5.000
-2048
-10.000
-2049
-10.0048
-4095
-19.995
<-4095
-20.000
464-8MC11
(4x±10 V)
464-8MD11
(4x±20 mA)
11-6
High Byte
7
6
5
4
11
10
9
S
2
2
2
Sign bit
0="+", 1="-"
Irrelevant bits
Error bit
0= no wire break; 1=wire break
Overflow bit
0= Measured value 4095 units at the most
1= Measured value greater than or equal to 4096 units
High Byte
in mA
40.0
0 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1
39.9902
0
1
1
1
1
20.0098
0
1
0
0
0
20.0
0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
10.0
0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
0.0098
0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0
0.0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
-0.0098
1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0
-10.0
1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0
-20.0
1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
-20.0098
1 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0
- 39.9902
1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0
-40.0
1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1
3
2
1
0
7
8
7
6
5
4
2
2
2
2
2
Low Byte
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
0
Low Byte
6
5
4
3
2
3
2
1
0
2
2
2
2
X
Range
Overflow
0
0
Overrange
0
0
Nominal range
Overrange
Overflow
EWA 4NEB 812 6210-02
S5-95F
1
0
E
OV
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