X20 system modules • Digital signal processing modules • X20DS1928
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X20 system User's Manual 3.10
Details
It is recommended to store transmitted messages in separate receive arrays.
After a set MessageEndBit is transmitted, the subsequent segment should be added to the receive array. The
message is then complete and can be passed on internally for further processing. A new/separate array should
be created for the next message.
Information:
When transmitting with MultiSegmentMTUs, it is possible for several small messages to be part of one
sequence. In the program, it's important to make sure that a sufficient number of receive arrays can
be managed. The entire sequence must be accepted before it is possible to change the Acknowledge
register.
If a SequenceCounter is incremented by more than one value, then an error has occurred
(this situation is very
unlikely when operating without "Forward" functionality).
In this case, the receiver stops. All additional incoming sequences are ignored until the transmission with the correct
SequenceCounter is retried. This response prevents the transmitter from receiving any more acknowledgments for
transmitted sequences. The transmitter can identify the last successfully transmitted sequence from the opposite
station's SequenceAck and continue the transmission from this point.
Acknowledgments must be checked for validity.
If the receiver has successfully accepted a sequence, it must be acknowledged. The receiver takes on the Se-
quenceCounter value sent along with the transmission and matches the SequenceAck to it. The transmitter reads
the SequenceAck and registers the successful transmission. If the transmitter acknowledges a sequence that has
not yet been dispatched, then the transmission needs to be interrupted and the channel resynchronized. The syn-
chronization bits are reset and the current/incomplete message is discarded. It needs to be sent again once the
channel has been resynchronized.
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