X20CM4800X - Data sheet V1.04
Fig.: Relationship between OutputSequence and InputSequence
Registers OutputSequence and InputSequence are logically composed of 2 half-bytes. The low part signals to the opposite station whether a channel should be opened or if data should be accepted. The high part is to acknowledge that the requested action was carried out.
SyncBit and SyncAck
If SyncBit and SyncAck are set in one communication direction, then the channel is considered "synchronized", i.e. it is possible to send messages in this direction. The status bit of the opposite station must be checked cyclically. If SyncAck has been reset, then SyncBit on that station must be adjusted. Before new data can be transferred, the channel must be resynchronized.
SequenceCounter and SequenceAck
The communication partners cyclically check whether the low nibble on the opposite station changes. When one of the communication partners finishes writing a new sequence to the MTU, it increments its SequenceCounter. The current sequence is then transmitted to the receiver, which acknowledges its receipt with SequenceAck. In this way, a "handshake" is initiated.
Information:
If communication is interrupted, segments from the unfinished message are discarded. All messages that were transferred completely are processed.