Process Images And Process Image Partitions; Process Image - Overview - Siemens SIMATIC S7-1500 System Manual

Configuring
6.1 Configuring the CPU
Value status
The value status is additional binary information of an analog input or output value. It is
entered simultaneously with the process value in the process image input and provides
information about the validity of the analog value.
If you enable the value status for an analog module, then additional bytes are allocated in
the input address area. Each bit in the value status is assigned to a channel and provides
information about the validity of the process value. You can find the assignment in the
product manual for the respective I/O module.
The value status is influenced by all diagnostics that might falsify the process value, e.g. wire
break, short-circuit.
● 1
● 0
or inaccessible.
Reference
Additional information on addressing and address allocation with value status can be found
in the manuals of the analog modules, and in the online help for STEP 7. A detailed
description of the value status for analog modules is available in the function manual Analog
value processing (http://support.automation.siemens.com/WW/view/en/67989094). An
example of the evaluation of the value status in the user program is available in the function
manual Diagnostics (http://support.automation.siemens.com/WW/view/en/59192926).
6.1.3

Process images and process image partitions

6.1.3.1

Process image - overview

Process image of the inputs and outputs
When the user program addresses the input (I) and output (O) operand areas, it does not
query the signal states directly from the I/O modules. Instead, it accesses a memory area of
the CPU. This memory area contains an image of the signal states and is called the process
image.
Advantages of the process image
A process image allows you to access a consistent image of process signals during cyclic
program execution. If a signal state at an input module changes during program processing,
the signal state is retained in the process image. The process image is not updated until the
next cycle.
112
: A valid process value is being output or read for the channel.
B
: A substitute value is being output for the channel, or the channel is deactivated, faulty
B
Automation system
System Manual, 09/2016, A5E03461182-AD