Pdo transmission types: parameterisation – BECKHOFF FC5101 User Manual
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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 type
Cyclical
Acyclical
Synchronous
Asynchronous
Only RTR
0
X
X
1-240
X
X
241-251
- reserved -
252
X
X
253
X
X
254, 255
X
The type of transmission is parameterised for RxPDOs in the objects at 0x1400ff, subindex 2, and for TxPDOs
in the objects at 0x1800ff, subindex 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 rea-
sons 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
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