Image Processing Reference
In-Depth Information
same device to be collected in the same CAN frame. Obviously, the information that are gathered
in the same PDO must have the same direction (transmission/reception) and triggering scheme
(including periodicity). Moreover, their overall size cannot exceed  bytes.
Two kinds of PDO mapping can be provided, that is static and dynamic. Static mapping is built-in
in the device and cannot be changed, whereas dynamic mapping can be freely configured by accessing
the OD through SDOs. Mapping parameters for RPDOs and TPDOs are stored in the OD in entries
 h -FF h and A h -BFF h ,respectively.
15.6.4 Service Data Objects
SDOsprovidedirectaccessforreadingandwritingentriesoftheOD.heyareusedinCANopen
for parameterization and configuration activities, which usually take place at a lower priority than
process data (they are considered nonreal-time exchanges). In this case, a confirmed transmission
service is required, which ensures a reliable exchange of information. Furthermore, SDOs are only
available on a peer-to-peer client/server communication basis (multicasting is not allowed).
A fragmentation protocol has been defined for SDOs—that comes from the domain transfer ser-
vices of CAL—so that information of any size can be exchanged. his means that the SDO sender has
to split the information is smaller chunks (fragments), which are then reassembled at the receiver's
side. his affects the communication efficiency negatively. However, as SDOs are seldom used for the
real-time control of the system, this is not perceived as a real problem.
SDOsareusedbyapplicationsand/orconigurationtoolstoaccesstheentriesoftheOD.Froma
practical point of view, two services are provided, which are used to upload and download the content
of one subentry of the OD, respectively. SDO transfers are always initiated on the client side of the
connection and the related protocol relies on CAN frames having an -byte payload.
Three kinds of transfers are envisaged for SDOs, namely expedited, normal (segmented),
and block.
An expedited transfer is a particular (simplified) case of SDO that requires only two frame
exchanges between the client and the server (i.e., SDO download/upload initiate request and
response). As a consequence, however, only up to  bytes of data can be exchanged.
A normal transfer is based on a segmented approach. In this case, following the SDO down-
load/upload initiate message pair, a variable number of fragments is sent, each one by means of an
SDO download/upload request/response pair.
Block transfer is an optional mode where information is exchanged as a sequence of blocks, each
one consisting of a sequence of up to  segments. A go-back-n strategy is adopted in this case to
confirm the correct delivery of each block, in order to improve the efficiency in transferring large
amounts of data.
In CANopen each node must provide SDO server functionalities. his means that it has to define
a pair of COB-IDs to support remote access to its OD, one for each direction of the transfer.
Generally speaking, only one SDO client at a time is allowed in the network; in practice, only
one SDO client is enabled to connect to any SDO server, and this is implicitly guaranteed with the
static approach foreseen in the predefined connection set. Optionally, the dynamic establishment of
additional SDO connections can be provided by means of a network entity called the SDO manager.
15.6.5 Other Objects
15.6.5.1 Synchronization Object
The SYNC object is periodically broadcast over the network by the SYNC producer, and is aimed at
enabling synchronous operation. he time elapsing between any two subsequent generations of the
SYNC message can be configured through the communication cycle period (expressed in µs).
 
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