Siemens SIMATIC S7-1500 Function Manual page 14

Just-In-Time
Figure 2-1
The fast and reliable reaction time of a system operating in isochronous mode is based on
the fact that all data are provided just-in-time. The basis for this is a constant bus cycle.
The isochronous mode function guarantees synchronization of the following at constant time
intervals:
● Signal acquisition and output by the central and distributed I/O
● Signal transmission via backplane bus, PROFINET IO or PROFIBUS DP
● Program execution in the CPU in local time, in time with the constant bus cycle time
PROFINET IO or PROFIBUS DP
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 reaction times as well as constant bus cycle and synchronous signal
processing for central and distributed I/O.
Isochronous mode
Function Manual, 10/2018, A5E43884988-AA
System cycle
What is isochronous mode?
13