XPS/XPS-E User's Manual Contents
COMSOFT 19
1. The data_exchange.req is transmitted to the XPS/XPS-E.
XPS/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.
2. Next
data_exchange.req service. XPS/PS-E responds with the
old data. New data are in fact received, but they do not contain the
trigger character.
3. Next
data_exchange.req service. XPS/PS-E responds with the
old data, because no further serial data were received.
4. Next
data_exchange.req service. XPS/PS-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.
3.2.3 Request Mode
In the request mode the XPS/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/XPS-E confirmation number is incremented by
one and returned in the response telegram (as in the poll mode).
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.
Note:
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