Beckhoff CX1500-B310, Руководство пользователя

Страница: 102 / 182

Product overview
CX1500-M510, CX1500-B510 102 Version: 1.0
The transmission types 254 + 255 are asynchronous, but may also be event-driven. In transmission type
254, the event is specific to the manufacturer, whereas for type 255 it is defined in the device profile. In the
simplest case, the event is the change of an input value - this means that every change in the value is
transmitted. The asynchronous transmission type can be coupled with the event timer, thus also providing
input data when no event has just occurred.
Inhibit time
Inhibit time
The ”inhibit time" parameter can be used to implement a ”transmit filter" that does not increase the reaction
time for relatively new input alterations, but is active for changes that follow immediately afterwards. The
inhibit time (transmit delay time) specifies the minimum length of time that must be allowed to elapse
between the transmission of two of the same telegrams. If the inhibit time is used, the maximum bus loading
can be determined, so that the worst case latency can then be found.
Although the BECKHOFF FC510x PC cards can parameterize the inhibit time on slave devices, they do not
themselves support it. The transmitted PDOs become automatically spread out (transmit delay) as a result of
the selected PLC cycle time - and there is little value in having the PLC run faster than the bus bandwidth
permits. The bus loading, furthermore, can be significantly affected by the synchronous communication.
Event Timer
Event Timer
An event timer for transmit PDOs can be specified by sub-index 5 in the communication parameters. Expiry
of this timer is treated as an additional event for the corresponding PDO, so that the PDO will then be
transmitted. If the application event occurs during a timer period, it will also be transmitted, and the timer is
reset.