Appendix; Configuration Of Cycle Times - IBA ibaFOB-TDCexp Manual

ibaFOB-TDCexp

Appendix

11

Configuration of cycle times

11.1
The cycle times can be automatically calculated by ibaPDA depending on the configured
channels, the requested signals and the cycle times of the connected CPUs. You can
also manually configure these cycle times. Each cycle time must be a multiple of the
base cycle time (T1).
Example
The figure shows how the channels are read. In the example there are 3 time classes
with different transfer durations:
 T1=2 ms, transfer duration 0.2 ms
 T2=4 ms, transfer duration 0.5 ms
 T3=8 ms, transfer duration 1.6 ms.
The card tries to start a data transfer for each cycle time of T1, i.e., every 2 ms. If this
cycle time coincides with the cycle time of another time class then the transfer for that
time class is performed as well. If there is already a transfer busy when cycle time T1 is
activated then the transfer scheduled to start at that time is not performed.
In the above-mentioned example at t=0 ms the cycle times for T1, T2 and T3 all coincide
so a transfer is started that reads data for T1, T2 and T3. This transfer takes 0.2 ms
+ 0.5 ms + 1.6 ms = 2.3 ms.
Thus at t=2 ms the transfer is still busy when the next cycle time starts; as a result the
transfer which should read data from T1 at t=2 ms is skipped.
At t=4ms a new transfer is started that reads data from T1 and T2. This takes 0.2 ms
+ 0.5 ms = 0.7 ms.
At t=6 ms a new transfer is started that reads data from just T1. This one takes 0.2 ms.
At t=8 ms the same procedure is executed as at t=0 ms.
In this example there is 1 transfer skipped every 4 transfers for time class T1. For all the
other time classes no transfers are skipped.
On the "Timing" tab the rate of valid transfers will be 75% for T1 and 100% for T2 and
T3. The current transfer duration shows the time it took the last transfer to be completed.
The max transfer duration gives you an idea on how long the transfer takes when the
reads for all time classes coincide. If this duration is longer than the T1 cycle time then
T1 transfers will be dropped. If it is longer than the T2 cycle time then T2 transfers will
be dropped as well.
Manual
Issue 1.2
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