CANopen system overview
CXxxxx-M510/B510
16
Version: 1.0
As from CANopen Version 4 it is possible to combine the event driven type of communication with a
cyclic update. The process data objects (in this case the TxPDOs) are then transferred once a set time
(event timer) has elapsed. If an input value changes within the set time, the time (event timer) is reset.
With RxPDOs the set time (event timer) is used to monitor the arrival of the event-driven process data
objects (PDOs). A device switches to error state, if no process data objects (PDOs) arrived within the
set time.
•
Polled:
The process data objects (PDOs) are polled through request telegrams (remote frames). In this way
the process data objects (PDOs) are transferred even if there is no change, for sample if a monitor or
diagnostic device is included in the network at runtime.
Function blocks with integrated full message filtering (FullCAN) usually respond to a request telegram
directly and immediately send the data contained in the corresponding send buffer. The application
must ensure that the data are continuously updated. CAN controllers with simple message filtering
(BasicCAN) on the other hand pass the request on to the application which can now compose the
telegram with the latest data. This does take longer, but does mean that the data is up-to-date.
Beckhoff use CAN controllers following the principle of Basic CAN.
Since this device behavior is usually not transparent to the user, and because there are CAN
controllers still in use that do not support remote frames at all, polled communication will only with
reservation be recommended for operative running.
•
Synchronized
It is not only for drive applications that it is worthwhile to synchronize the determination of the input
information and the setting the outputs. For this purpose CANopen provides the SYNC object, a CAN
telegram of high priority but containing no user data, whose reception is used by the synchronized
users as a trigger for reading the inputs or for setting the outputs.
PDO transmission types: Parameterization
The PDO transmission type determines how the transfer of the process data objects (PDOs) is triggered and
how the received process data objects (PDOs) are treated:
Transmission
type
Cyclical
Acyclical
Synchronous
Asynchronous
0
X
X
1-240
X
X
254, 255
X
The type of transmission is parameterized for RxPDOs in the objects at 0x1400ff, sub-index 2, and for
TxPDOs in the objects at 0x1800ff, sub-index 2. In TwinCAT the PDO transmission type is set on the PDO
tab under Transmission Type (see:
•
Acyclic Synchronous:
PDOs of transmission type 0 function synchronously, but not cyclically. An RxPDO is only evaluated
after the next SYNC telegram. In this way, for instance, axis groups can be given new target positions
one after another, but these positions only become valid at the next SYNC - without the need to be
constantly outputting reference points.
In contrast, a TxPDO determines its input data after a SYNC telegram (synchronous process image)
and forwards its input data if the input data have changed.
Transmission type 0 therefore combines the send reason „synchronized“ with the send reason “event-
driven”.
•
Cyclic Synchronous:
With transmission types 1-240 the PDO is sent cyclically after each n-th SYNC (n=1...240). In this way
it is possible to parameterise a fast cycle for digital inputs (n=1), for sample, while the data of the
analog inputs are transferred in a slower cycle (e.g. n=10). RxPDOs generally do not differentiate
between the transmission types 0...240. A received PDO is set to valid with the next SYNC telegram.
Содержание CX-B510 Series
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