Principles Of Analog Modules - Siemens SIMATIC Manual

Principles of analog modules

Introduction
This chapter describes the analog values for all measuring or output ranges supported by
the analog modules.
Analog value conversion
The CPU always processes the analog values in binary format.
Analog input modules convert the analog process signal to a digital format.
Analog output modules convert digital output values to analog signals.
Representation of analog values at a resolution of 16 bits
The digitized analog value applies to input and output values of the same rated range.
Analog values are output as fixed point numbers with two's complement. The resultant
assignment:
Bit 15
15
Bit values 2
Sign
The sign of the analog value is always set at bit 15:
● "0" → +
● "1" → -
Resolution < 16 bits
On analog modules with a resolution of < 16 bits, the analog value is stored left-aligned. The
unused least significant bit positions are padded with zeros ("0".)
Example
The example below demonstrates the zero padding of unused bit positions for low resolution
values.
Table 5- 1 Example: Bit pattern of a 16-bit and 13-bit analog value
Resolution
Bit
16-bit analog value
13-bit analog value
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ
14 13 12 11
14 13 12 11
2 2 2 2
Analog value
15 14 13 12
0 1 0 0
0 1 0 0
10 9 8 7
10 9 8 7
2 2 2 2
11 10 9 8
0 1 1 0
0 1 1 0
6 5 4 3
6 5 4 3
2 2 2 2
7 6 5 4 3
0 1 1 1 0
0 1 1 1 0
5
2 1 0
2 1 0
2 2 2
2 1 0
0 1 1
0 0 0
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