X20 system modules • Digital signal processing modules • X20DS1928
X20 system User's Manual 3.10
1441
Large segments and MultiSegmentMTU:
Example:
Three autonomous messages (7 bytes, 2 bytes, 9 bytes) are being transferred using an MTU with a width of 7 bytes.
The configuration allows the transfer of large segments as well as MultiSegmentMTUs.
Message 1:
A1
A2
A3
A4
A5
A6
A7
B1
B2
D1
D2
D3
D4
D5
D6
D7
D8
No more data to transmit
-
-
...
-
Message 2:
Message 3:
Sequence for bus cycle 1
Sequence for bus cycle 2
Sequence for bus cycle 3
Sequence for bus cycle 4
Sequence for bus cycle 5
Sequence for bus cycle 6
D9
A2
A3
A4
A1
A5
A6
C1
A7
C2
B1
B2
C3
D1
D2
D3
D4
D5
D6
D7
D8
-
-
C0
-
-
-
-
-
C0
-
-
-
-
-
-
C0
-
-
-
-
Both options
-
D9
Transmit/Receive array
With 7 USINT elements according to
the configurable MTU size
Figure 448: Transmit/Receive array (large segments and MultiSegmentMTU)
First, the messages must be split into segments. If the last segment of a message doesn't completely fill the MTU,
it can be used for other data in the data stream. The "nextCBPos" bit must always be set if the control byte belongs
to a segment with payload data.
The ability to form large segments means that messages are split up less frequently, which results in fewer gen-
erated control bytes. Control bytes are generated in the same way as with the "Large segments" option.
Large segments allowed → Max. segment length = 63 bytes
•
Message 1 (7 bytes)
➯
First segment = Control byte + 7 data bytes
•
Message 2 (2 bytes)
➯
First segment = Control byte + 2 data bytes
•
Message 3 (9 bytes)
➯
First segment = Control byte + 9 data bytes
•
No more messages
➯
C0 control byte
A unique control byte must be generated for each segment. In addition, the C0 control byte is generated to keep
communication on standby.
C1 (control byte 1)
C2 (control byte 2)
C3 (control byte 3)
- SegmentLength (7)
=
7 - SegmentLength (2)
=
2 - SegmentLength (9)
=
9
- nextCBPos (0)
=
0 - nextCBPos (0)
=
0 - nextCBPos (0)
=
0
- MessageEndBit (1)
=
128 - MessageEndBit (1)
=
128 - MessageEndBit (1)
=
128
Control byte
Σ
135 Control byte
Σ
130 Control byte
Σ
137
Table 444: FlatStream determination of the control bytes for large segments and MultiSegmentMTU example
Summary of Contents for X20 System
Page 2: ......
