X20 system modules • Analog input modules • X20AI2438
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X20 system User's Manual 3.10
Details/Background:
1. Illegal SequenceCounter size (counter offset)
Error situation: MTU not enabled
If the difference between SequenceCounter and SequenceAck is larger than allowed during transmission,
then a transmission error has occurred. In this case, all unacknowledged sequences must be repeated with
the old SequenceCounter value.
2. Checking an acknowledgment
After an acknowledgment has been received, a check must verify whether the acknowledged sequence has
been transmitted and had not yet been unacknowledged. If a sequence has been acknowledged more than
once, then a fatal error has occurred. The channel must be closed and resynchronized (same behavior as
when not using Forward).
Information:
In exceptional cases, the module can increment OutputSequenceAck by more than 1 when using
Forward.
This is not an error. The CPU is permitted to consider all sequences up to the one being acknowl-
edged as having been transmitted successfully.
3. Transmit and receive arrays
The Forward function has no effect on the structure of the transmit and receive arrays. They are created and
must be evaluated in the same way.
