The Timing (Online/Offline) Tab; Fig. 8 The Timing (Offline) Tab - Beckhoff FC7501 Documentation

Configuration
T3 User
The value set here alters the time T3 used in the internal time slot calculation.
T4 User
The value set here alters the time T4 used in the internal time slot calculation.
4.3

The Timing (Online/Offline) tab

Fig. 8: The Timing (Offline) tab
The Timing tab provides internal details of the time slot calculation. A distinction is made between an online
and an offline mode, since parameters are also read from the devices and included in the calculation of the
time slot. In offline mode (TwinCAT is stopped) default values are used for the timing values that are
normally read from the devices, so that the result of this calculation can differ slightly from that obtained with
the true values. The offline calculation does however as a rule provide a very good estimate of the bus
timing. In online mode (TwinCAT is running and the Sercos Bus is in phase 3 or 4) the exact values are
displayed, and provide the expert user with very precise information about the timing on the bus.
The diagram in the lower section provides a good summary of the bus loading being generated, and over the
capacity still available. A Sercos cycle is displayed between the two red master control telegrams (MST).
After the MST the devices first send their drive telegrams (green), and after the NC shift time the NC access
time (dotted region) starts, in which the NC accepts the actual values and transmits new set values. The
subsequent clear region leading up to the Master Data Telegram (MDT, blue) indicates "bus capacity that is
still free", and can be used for other devices or for additional data associated with the existing devices.
Not long after the MDT the master sends another MST, so starting the next cycle. Times T3 and T4 indicate
when the devices should all simultaneously accept the set values or acquire the actual values.
16 Version: 2.0 FC7501 and FC7502