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S5-100U
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 one of
the following ways:
•
In one byte (466-8MA11)
•
In two bytes (the remaining analog input modules)
Each bit position has a fixed value in powers of two (see Tables 11-4 and 11-14). Analog values
are represented in two's complement.
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 11-4. Representation of an Analog Input Value as Bit Pattern
Bit Number
Analog Value Represent.
Key:
S
X
E
OV
Analog value representation for analog input modules 464-8...
Table 11-5. Analog Input Module 464-8MA11, -8MF11, -8MB11 (Bipolar Fixed-Point Number)
Measured Value
Units
>4095
100.0
4095
99.976
2049
50.024
2048
50.0
1024
25.0
1
0.024
0
0.0
-1
- 0.024
-1024
- 25.0
-2048
-50.0
-2049
-50.024
-4095
-99.976
<-4095
-100.0
464-8MA11/-8MA21 "No linearization"
464-8MF11
(2x±500 mV)
464-8MB11
(4x±1 V)
EWA 4NEB 812 6120-02
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
in mV
1000.0
2000.0
0 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1
999.75
1999.5
0
1
500.24
1000.48
0
1
500.0
1000.0
0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
250.0
500.0
0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
0.24
0.48
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 0
-0.24
-0.48
1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0
- 250.0
- 500.0
1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0
-500.0
-1000.0
1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
-500.24
-1000.48
1 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0
-999.75
-1999.5
1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0
-1000.0
-2000.0
1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1
(4x±50 mV)
3
2
1
0
7
8
7
6
5
4
2
2
2
2
2
High Byte
Low Byte
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
Analog Value Processing
Low Byte
6
5
4
3
2
3
2
1
0
2
2
2
2
X
Range
Overflow
1
1
1
0
0
0
Overrange
0
0
1
0
0
0
Nominal range
Overrange
Overflow
1
0
E
OV
11-11
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