XPS-E
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NOTICE
Please note, that it is not necessary to set the receive request number (X)
in polling/serial Mode
1. The data_exchange.req is transmitted to the XPS-E. XPS-E has already
received data via the serial interface. This data are transmitted with
data_exchange.res back to the DP-Master. The receive confirmation
number is incremented and data length and status are updated.
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2. Next data_exchange.req service. XPS-E responds with the old data.
New data are in fact received, but they do not contain the trigger
character.
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3. Next data_exchange.req service. XPS-E responds with the old data,
because no further serial data were received.
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4. Next data_exchange.req service. XPS-E has received in the meantime
the serial trigger character. The receive confirmation number is
incremented, data length, status and data_exchange.res buffer are
updated with the actual data.
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Request-Mode
In the request mode the XPS-E only sends receive data if a modified
receive-request number is contained in the request telegram. The
data are not returned in the first response telegram but in the
response telegram of the subsequent data_exchange service. This
means that the data are returned always only in the subsequent
cycle of the request. If the response telegram contains received data,
the XPS-E confirmation number is incremented by one and returned
in the response telegram (as in the poll mode).
NOTICE
If this mode is used while the master is automatically polling the slaves
according to the poll list, the data that have been received last remain in the
process image
Data exchange