X20 system modules • X20 electronics module communication • X20CS2770
X20 system User's Manual 3.10
1693
MultiSegmentMTUs allowed
With this option, the InputMTU is completely filled (if enough data is pending). The previously unfilled Rx bytes
transmit the next control bytes and their segments. This allows the enabled Rx bytes to be used more efficiently.
Bus cycle 1
Control byte with MessageEndBit = 0
Bus cycle 2
Bus cycle 3
-
-
ME1
C
ME1
C
ME0
C
ME1
C
Control byte with MessageEndBit = 1
Segment 1
Segment 2
Segment 4
Message 1
Message 2
ME0
C
ME0
C
3
Figure 534: Arrangement of messages in the MTU (MultiSegmentMTUs)
Large segments allowed
When transmitting very long messages or when enabling only very few Rx bytes, then a great many segments must
be created by default. The bus system is more stressed than necessary since an additional control byte needs to
be created and transmitted for each segment. With the "Large segments" option, the segment length is limited to
63 bytes independently of the InputMTU. One segment can stretch across several sequences, i.e. it is possible for
"pure" sequences to occur without a control byte.
Information:
It is still possible to split up a message into several segments, however. If this option is used and
messages with more than 63 bytes occur, for example, then messages can still be split up among
several segments.
Bus cycle 1
Control byte with MessageEndBit = 0
Bus cycle 2
Bus cycle 3
-
-
-
ME1
C
ME1
C
ME0
C
ME1
C
Control byte with MessageEndBit = 1
Segment 1
Segment 2
Segment 3
Message 1
Message 2
-
Figure 535: Arrangement of messages in the MTU (large segments)
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