Siemens SIMATIC User Manual

S7-300 Module data
Manual, 06/2017, A5E00105505-AJ
261
Principles of analog modules
5
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
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Bit values
2
15
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 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
Analog value
Bit
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
16-bit analog value
0
1
0
0
0
1
1
0
0
1
1
1
0
0
1
1
13-bit analog value
0
1
0
0
0
1
1
0
0
1
1
1
0
0
0
0

Siemens SIMATIC Specifications

General

Product type designation	SIMATIC
CPU	Varies by model
Memory	Varies by model
Input/Output	Varies by model
Communication	Varies by model
Programming Language	STEP 7
Operating Temperature	0°C to 60°C (varies by model)
Protection Class	IP20
Category	Programmable Logic Controller (PLC)