Siemens SIMATIC ET 200AL, System Manual

Page: 1783 / 2255

Functions
5.7 Isochronous mode
PROFINET with STEP 7
218
Function Manual, 05/2021, A5E03444486-AL
The fast and reliable response time of a system operating in isochronous mode is due to the
fact that all data is provided just-in-time. The basis for this is an equidistant cycle.
The isochronous mode function guarantees synchronization of the following at constant time
intervals:
•
Signal acquisition and output by the distributed I/O
• Signal transmission via PROFINET IO
• Program execution in the CPU in time with the equidistant PROFINET IO
The result is a system that acquires its input signals, processes them and outputs the output
signals at constant time intervals. Isochronous mode guarantees precisely reproducible and
defined process response times as well as equidistant and synchronous signal processing for
distributed I/O.
Advantages of isochronous mode
The use of isochronous mode allows high-precision control.
•
Optimized control loops through constant, calculable dead times
• Determinism, reliable reproducibility of response times
• Consistent (simultaneous) reading in of input data
• Consistent (simultaneous) output of output data
5.7.2 Use of isochronous mode
An isochronous system acquires measured values and process data within a fixed system
cycle, processes the signals and outputs them synchronously to the process. Isochronous
mode contributes to a high control quality and increased production accuracy. With
isochronous mode, the possible fluctuations of process response times are drastically
reduced. You make use of the time-assured processing to improve machine cycle times. Even
fast processes can be reliably controlled thanks to the precise time reproducibility of all
sequences. Shorter cycle times increase the processing speed and help to lower production
costs.
In principle, isochronous mode is worthwhile whenever measured values must be acquired
synchronously, movements must be coordinated, and process responses must be defined and
simultaneously executed, as in the following example. Isochronous mode can thus be used in
a wide variety of applications.