S5-100U 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 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
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
10
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
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
Analog value representation for analog input modules 464-8...
Table 11-5. Analog Input Module 464-8MA11, -8MF11, -8MB11 (Bipolar Fixed-Point Number)
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Units
Measured Value
in mV
High Byte Low Byte Range
>4095 100.0 1000.0 2000.0 0 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1 Overflow
4095
2049
99.976
50.024
999.75
500.24
1999.5
1000.48
0
0
1
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
1
0
0
0
0
0
0
Overrange
2048 50.0 500.0 1000.0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1024 25.0 250.0 500.0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
1 0.024 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 0 0 Nominal range
-1 - 0.024 -0.24 -0.48 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0
-1024 - 25.0 - 250.0 - 500.0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0
-2048 -50.0 -500.0 -1000.0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
-2049 -50.024 -500.24 -1000.48 1 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 Overrange
-4095 -99.976 -999.75 -1999.5 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0
<-4095 -100.0
-1000.0 -2000.0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 Overflow
464-8MA11/-8MA21 “No linearization” (4x±50 mV)
464-8MF11 (2x±500 mV)
464-8MB11 (4x±1 V)
EWA 4NEB 812 6120-02
11-11
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