Configuration of Polled Data Exchange
The Polled Data Exchange mode is configured with the help of the EAP Object Dictionary. To do this the RxPD which, as a client, is to receive the response of the server must be configured in one EAP device, while the TxPD which, as a server, defines the response to the client's request must be configured in another EAP device.
As shown in the following illustration, a TxPD is configured on the client side for the request and is cyclically transmitted as in Pushed Data Exchange mode. For receiving the server response, two RxPDs are configured on the client side in this sample. With both RxPDs the index of the TxPD that serves as the request is entered in the Poll Request TxPD property . On the basis of the transmission time of the request, an RxPD can determine a quality value on whose basis the time difference between request and response can be read.
On the server side, an RxPD is configured for the reception of the request that works as in Pushed Data Exchange mode. In this example two TxPDs are configured for the transmission of the response to the client request. With both TxPDs the index of the RxPD that serves as the recipient of the request is entered in the Poll Request RxPD property. In each processing cycle a TxPD checks with its configured Poll Request RxPD whether a request has been received. If so, the TxPD is sent back in this cycle as the response.
