POWERLINK Information
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06/21/2018
3.7 Transmission of SDO messages
The entries of the object dictionary can be read or written with the SDO services. The
SDO Transport Protocol allows the transmission of objects of any size.
Services with confirmation (Initiate SDO Upload, Initiate SDO Download, Download
SDO Segment, and Upload SDO Segment) and services without confirmation (Abort
SDO Transfer) are used for the execution of Segmented/Expedited transmission of
Service Data Objects.
The so-called
SDO Client
(MN) specifies in its “Request” the parameter, the access
type (read/write) and the value if applicable. The so-called
SDO Server
(CN or
measuring system) executes the write or read access and answers the request with a
“Response”. In the case of error, an error code (Abort SDO Transfer) provides
information on the cause of the error.
The measuring system supports SDO transmissions over
UDP/IP and EPL Asnd
frames
in the asynchronous time period.
MAC-Frame-Header
(EtherType = 0800h)
IP-Header
(Protocol = 0x11)
UDP-Header
(Port = 0xXXXX)
EPL Content
CRC
Figure 6: EPL compliant UDP/IP frame structure
Normally the POWERLINK master provides appropriate mechanisms for the SDO
transfer. Knowledge of the protocol structure and internal sequences is therefore not
required.
3.8 Abort SDO Transfer Protocol
An Abort SDO Transfer request/indication, indicating the unsuccessful completion of
the SDO Upload or Download sequence. The Abort service is unconfirmed and may
be executed at any time by either the client or the server of a SDO. The protocol
contains a 4-byte-error code which provides information on the cause of the error, see
Table 7 on page 83.
Bit Offset
Byte
Offset
7
6
5
4
3
2
1
0
0
reserved
1
Transaction ID
2
Res-
ponse
Abort =
1
Segmentation
reserved
3
Command ID
4-5
Segment Size
6-7
reserved
8-11
Abort Code
Figure 7: Abort Transfer Frame
