
APPENDIX
Serial Bus Protocol
2.10
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19.01.2007
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5.3.4.2 Ethernet Frame Structure
The frame used with serial bus protocol is structured similar to an ethernet frame.
DestAddr
(6 Byte)
SourceAddr
(6 Byte)
Type/Len
(2 Byte)
Data
(max. 1500 Byte)
The order of transmission is from left to right.
DestAddr
Destination address. B0 send out first.
SourceAddr
Source address. B0 send out first.
Type/Len
Ethernet uses this field for different purposes. If the value is not
larger than 1500 it indicates the data field length, if it is larger than
1500 it indicates the contained protocol. The MSB is transmitted first.
The radio system does not interpret the Type/Len field but accepts
all following bytes up to the physical frame end as data bytes. The
bus protocol may therefore use the Type/Len field at discretion.
Considering a real ethernet application however, the use according
to ethernet specification is recommended, i.e. using it as a length
indicator in the easy way.
Data
User data (max. 1500 bytes)
The ethernet preamble and the 32 bit CRC checksum are not covered here. Usually the
interface controller hardware of ethernet devices will generate and analyse theses fields
automatically. They are not transmitted during the transfer on a serial interface as described
below.
5.3.4.3 Format at the serial Interface
For the transmission of ethernet frames through a serial interface a HDLC frame format is
used. Only so called UI frames are used, which does not require acknowledge messages.
I.e. it is not necessary to implement a protocol on the host devices, only the frame format
must be supported.
Transmission is done byte-wise in the order of byte numbers. Bit 0 is LSB. The following
frame type is applied:
Byte No. Name
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
1
Flag
0
1
1
1
1
1
1
0
2
Addr
First
0
1
0
FrameNum
Last
1
3
Ctrl
0
0
0
0
0
0
1
1
4
Ethernet Frame Segment
...
ETH
...
L-3
Ethernet Frame Segment
L-2
CRC
HDLC CRC (low byte)
L-1
CRC
HDLC CRC (high byte)
L
Flag
0
1
1
1
1
1
1
0
Flag
Block Start identifier and Block End identifier.
Addr
The Addr byte in the HDLC frame will transport the following information: