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This means that data has to start at the next modulo 4 bytes. The rest of a 4-byte-block which is not covered by the number
of header bytes will not be transmitted.
Example1:
CHx_CNTRL1 = 0x20
The header field consist of a first byte which contains the number of header bytes (value = 4) and 4 header bytes, give in
total 5 bytes. The first 8 bytes comprise the header field. However the number byte and the last 3 bytes (of the 8 byte in total)
will be NOT transmitted.
byte 0: = 4
number of following header bytes (NOT transmitted!)
byte 1:
first header byte
byte 2:
second header byte
byte 3:
third header byte
byte 4:
forth header byte
byte 5:
ignored (NOT transmitted!)
byte 6:
ignored (NOT transmitted!)
byte 7:
ignored (NOT transmitted!)
byte 8:
first data byte
.
.
byte n:
last data byte
transmitted packet via SpaceWire:
byte 1 - byte 4
(4 header bytes)
byte 8 - byte n
(data bytes)
EOP
Example2: No data bytes, short packets
CHx_CNTRL1 = 0x20
The header field consist of a first byte which contains the number of header bytes (value = 2) and 2 header bytes, give in
total 3 bytes. The first 4 bytes comprise the header field. However the number byte and the last byte (of the 4 byte in total)
will be NOT transmitted.
byte 0: = 2
number of following header bytes (NOT transmitted!)
byte 1:
first header byte
byte 2:
second header byte
byte 3:
ignored (NOT transmitted!)
NO data byte
transmitted packet via SpaceWire:
byte 1
byte 2 (like data bytes)
EOP
Example3: with checksum generation
CHx_CNTRL1 = 0x30
The header field consist of a first byte which contains the number of header bytes excluded from checksum generation (value
=3) and 3 header bytes, give in total 4 bytes.
byte 0: = 3
number of following header bytes excluded from checksum (NOT transmitted!)
byte 1:
header byte
byte 2:
header byte
SMCS332SpW
User Manual
– All Rights Reserved – Copyright per DIN 34 –
EADS Astrium GmbH, ASE2
Doc No: SMCS_ASTD_UM_100
Issue:
1.4
Updated: 9-Sep-2006
Page:
52 of 131
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