Addressing The Analog Inputs (Ai); Addressing The Analog Outputs (Aq) - Siemens SIMATIC S7-200 System Manual

Addressing the Analog Inputs (AI)

The S7-200 converts a real-world, analog value (such as temperature or voltage)
into a word-length (16-bit) digital value. You access these values by the area
identifier (AI), size of the data (W), and the starting byte address. Since analog
inputs are words and always start on even-number bytes (such as 0, 2, or 4), you
access them with even-number byte addresses (such as AIW0, AIW2, or AIW4),
as shown in Figure 5-5. Analog input values are read-only values.
Format:
MSB
15
AIW8
Most significant byte
Figure 5-5

Addressing the Analog Outputs (AQ)

The S7-200 converts a word-length (16-bit) digital value into a current or voltage,
proportional to the digital value (such as for a current or voltage). You write these
values by the area identifier (AQ), size of the data (W), and the starting byte
address. Since analog outputs are words and always start on even-number bytes
(such as 0, 2, or 4), you write them with even-number byte addresses (such as
AQW0, AQW2, or AQW4), as shown in Figure 5-6. Analog output values are
write-only values.
Format:
MSB
15
AQW10
Most significant byte
Figure 5-6
S7-200 Programmable Controller System Manual
A5E00066097-02
CPU Memory: Data Types and Addressing Modes
AIW [starting byte address]
8 7
byte 8 byte 9
Least significant byte
Accessing an Analog Input
AQW [starting byte address]
8 7
byte 10 byte 11
Least significant byte
Accessing an Analog Output
AI W 8
LSB
Byte address
0
Access to a word-size value
Area identifier (analog input)
AQ W 10
LSB
Byte address
0
Access to a word-size value
Area identifier (analog output)
AIW4
AQW4
5-9