X20 system modules • Digital signal processing modules • X20DS1928
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X20 system User's Manual 3.10
MultiSegmentMTU allowed:
With this option, the InputMTU is completely filled (if enough data is pending). The previously unfilled Rx bytes
transfer the next control bytes and their segments. This allows the activated 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 443: Message arrangement in the MTU (MultiSegmentMTU)
Large segments allowed:
When transferring very long messages or when activating 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 transferred for every 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's 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, the 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 444: Message arrangement in the MTU (large segments)
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