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0198441113586, V2.01, 11.2008
IL•1F CANopen DS301 3 Basics
Fieldbus interface 27
3.3.3 SDO message
Put simply, an SDO message consists of the COB ID and the SDO data
frame, in which up to 4 bytes of data can be sent. Longer data se-
quences are distributed over multiple SDO messages with a special pro-
tocol.
The device sends SDOs of up to 4 bytes data length (data). Greater
amounts of data such as 8 byte values of the data type "Visible String 8"
can be distributed over multiple SDOs and are transmitted successively
in 7 byte blocks.
Example The following illustration shows an example of an SDO message.
Figure 3.11 SDO message, example
COB ID and data frame R_SDO and T_SDO have different COB IDs.
The data frame of an SDO messages consists of:
• Command code (ccd) in which the SDO message type and the data
length of the transmitted value are encrypted
• Index and subindex which point to the object whose data is trans-
ported with the SDO message
• Data of up to 4 bytes
Evaluation of numeric values Index and data are transmitted left-aligned in Intel format. If the SDO
contains numerical values of more than 1 byte in length, the data must
be rearranged byte-by-byte before and after a transmission.
Figure 3.12 Rearranging numeric values greater than 1 byte
Subindex
Index
Command Code
COB-ID
(581
h
)
1 2 3 4 5 6 7
00
0
43 10 00 01 0292 00
581
Data
SDO
00 02 01 92
h
10 00
h
Index:
Data:
Hex:
1 2 3 4 5 6 7
00
0
43 10 00 01 0292 00
581