Analog electronic modules
15.10 Analog value representation for measuring ranges with SIMATIC S7
ET 200pro distributed I/O system
Operating Instructions, 03/2013, A5E00335544-08
437
For further information on the "WRREC" SFB 53, refer to the manual titled System Software
for S7-300/400 System and Standard Functions
http://support.automation.siemens.com/WW/view/en/1214574
).
15.10
Analog value representation for measuring ranges with SIMATIC S7
Representation of analog values
With the same nominal range, the digitized analog value is the same for input and output
values. Analog values are visualized in two's complement.
The table below shows the visualization of the analog value of analog electronic modules.
Table 15- 1 Analog value visualization (SIMATIC S7 format)
Resolution
Analog value
Bit number
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Bit significance
Sign 2
14
2
13
2
12
2
11
2
10
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
Sign
The sign of the analog value is always set at bit number 15:
●
"0"
→
+
●
"1"
→
-
Measured value resolution
The table below shows the representation of binary analog values and of the associated
decimal and hexadecimal units of the analog values.
The table below shows the resolutions of 12, 13, 14, and 15 bits + sign. Each analog value is
written left aligned to the ACCU. The bits marked with "x" are set to "0".
Table 15- 2 Resolution of measured analog values (SIMATIC S7 format)
Resolution in bits
Units
Analog value
Decimal
Hexadecimal
High byte
Low byte
12+S
8
8
H
S 0 0 0 0 0 0 0
0 0 0 0 1 x x x
13+S
4
4
H
S 0 0 0 0 0 0 0
0 0 0 0 0 1 x x
14+S
2
2
H
S 0 0 0 0 0 0 0
0 0 0 0 0 0 1 x
15+S
1
1
H
S 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1
