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32 Fieldbus interface
3 Basics IL•1F CANopen DS301
0198441113586, V2.01, 11.2008
3.4.2 PDO data exchange
Figure 3.16 PDO data exchange
Data exchange with PDOs follows to the producer-consumer relation-
ship and can be triggered in 3 ways
• Synchronized
• Event-driven, asynchronous
• On request of a consumer, asynchronous
The SYNC object controls synchronized data processing. Synchronous
PDO messages are transmitted immediately like the standard PDO
messages, but are only evaluated on the next SYNC. For example, sev-
eral drives can be started simultaneously via synchronized data ex-
change.
The device immediately evaluates PDO messages that are called on re-
quest or in an event-driven way.
The transmission type can be specified separately for each PDO with
subindex 02
h
(transmission type) of the PDO communication parameter.
The objects are listed in 8 "Object directory".
Event-driven The "event" is a change of the PDO data. In this mode, the data is im-
mediately transmitted after a change. Please note that in the case of, for
example, a positioning movement, the actual position changes con-
stantly so that a large number of PDOs is transmitted. There are two
ways to avoid such a large number of PDOs:
• A) You can set an "Inhibit Timer" (object 1803
h
subindex 3). The
PDO is not sent until after this inhibit time has passed.
• B) By using a bit mask, you can limit the check for changes
(=event). See section "Bit mask for T_PDO4" for a description.
A further possibility of "creating" an event consists of activating an
"Event Timer" (object 1803
h
subindex 5). You activate this counter by en-
tering a value not equal to zero. When this counter is reached, this rep-
resents an additional event. This means that the PDO is transmitted
when a value changes or when the counter event occurs.
Synchronized In the case of this transmission mode, a PDO is transmitted in relation
to a SYNC object. See 3.5 "Synchronization" for a detailed description.
PDO Consumer
R_PDO
PDO Consumer
R_PDO
R_PDO
PDO Consumer
T_PDO
PDO Producer
COB-ID Data
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