Isochronous mode –
High-speed and precise processing operations
 SIMATIC S7-300, S7-400 and WinAC RTX permit that decentralized automation solutions can rely on high-speed processes and achieve maximum precision. The isochronous mode system function makes faster production possible while simultaneously increasing
quality.
Applications subject to such requirements include:
- Motion Control
- Synchronous operation
- Closed-loop controls
- Software-based cam control systems
- Measuring at several measuring points
- Speed and
- Flow measurement
The principle of the isochronous mode refers to synchronization of signal acquisition and output
by means of distributed I/Os, signal transmission over PROFIBUS
and program processing with the cycle of the equidistant
PROFIBUS. The result is a system which acquires and processes
its input signals and outputs its output signals at constant
intervals. S7-400 and S7-300 thus ensure exact reproducibility
and defined process response times, as well as equidistant and
synchronous signal processing with decentralized I/O devices.
The exact chronological reproducibility of all processes allows
even fast processes to be handled safely. A comprehensive
range of components which support the isochronous system
function is available to solve many applications in the areas of
motion control, measuring and controlling.
System without isochrone mode:
In many distributed automation structures, the processing cycles are
executed asynchronously:
- Read input signal (T1)
- Cycle for backplane bus of the ET 200 (T2, T6)
- DP cycle time (T3, T5)
- Program processing in the CPU (T4)
- Write output signal(T7)
System with isochrone mode:
With isochrone mode, these processes are embedded in a fixed time frame, the so-called system clock.
This results in the following system characteristics
- The input and output data are processed in an equidistant manner, i.e. in time intervals that remain constant
- Actualvalue sensing and setpoint output occur synchronously with the processing in the CPU
- This creates consistent process images
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