Beckhoff CX1500-M510 Manual page 101

PDO transmission types: Parameterisation
PDO transmission types: Parameterisation
The PDO transmission type parameter specifies how the transmission of the PDO is triggered, or how
received PDOs are handled.
Transmission Cyclical
type
0
1-240 X
241-251 - reserved -
252
253
254, 255
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.
Acyclic Synchronous
PDOs of transmission type 0 function synchronously, but not cyclically. An RxPDO is only evaluated after the
next SYNC telegram has been received. 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. A device whose TxPDO is configured for transmission type 0 acquires
its input data when it receives the SYNC (synchronous process image) and then transmits it if the data
correspond to an event (such as a change in input) having occurred. Transmission type 0 thus combines
transmission for reasons that are event driven with a time for transmission (and, as far as possible, sampling)
and processing given by the reception of "SYNC".
Cyclic Synchronous
Cyclic Synchronous
In transmission types 1-240 the PDO is transmitted cyclically: after every "nth" SYNC (n = 1...240). Since
transmission types can be combined on a device as well as in the network, it is possible, for example, for a
fast cycle to be agreed for digital inputs (n = 1), whereas the data for analog inputs is transmitted in a slower
cycle (e.g. n = 10). RxPDOs do not generally distinguish between transmission types 0...240: a PDO that has
been received is set to valid when the next SYNC is received. The cycle time (SYNC rate) can be monitored
(object 0x1006), so that if the SYNC fails the device reacts in accordance with the definition in the device
profile, and switches, for example, its outputs into the fault state.
The FC510x card provides full support for the synchronous type of communication: transmitting the SYNC
telegram is coupled to the linked task, so that new input data is available every time the task begins. The
card will recognize the absence of a synchronous PDO, and will report it to the application.
Only RTR
Transmission types 252 and 253 apply to process data objects that are transmitted exclusively on request by
a remote frame. 252 is synchronous: when the SYNC is received the process data is acquired. It is only
transmitted on request. 253 is asynchronous. The data here is acquired continuously, and transmitted on
request. This type of transmission is not generally recommended, because fetching input data from some
CAN controllers is only partially supported. Because, furthermore, the CAN controllers sometimes answer
remote frames automatically (without first requesting up-to-date input data), there are circumstances in which
it is questionable whether the polled data is up-to-date. Transmission types 252 and 253 are for this reason
not supported by the BECKHOFF PC cards.
Asynchronous
Asynchronous
CX1500-M510, CX1500-B510
Acyclical Synchronous
X X
X
X
Version: 1.0
Product overview
Asynchronous Only RTR
X
X X
X
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