Peripheral Devices
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Whenever one of these sequences is executed a new package of data is transferred to, or from, the
PowerMACS system.
Since most types of Process data are too big to fit into the available area it is split up into packages. Each
access will transfer a new package. The data part of the IN and the OUT areas are therefore further dived
into several fields in order to handle transferring sequence of packages.
See chapter: Process data for a detailed description of this. There is also described how the respective
Process data is formatted.
Normally no data is written to the Process Data out area unless the client first has requested so. However,
by checking the Load Cycle Data automatically check box for the fieldbus device (see System ) the
PowerMACS system will automatically load the first package of a cycle data when the cycle is finished.
The data will only be written if the Process Data out area is free for PowerMACS to write to. The area is
considered free as long as the fieldbus master do not already have a read or write transaction ongoing
(i.e. it have issued a command but not yet written zero (0) to the CMD word to indicate that it has read the
response). If a Cycle Data is generated when the output area is not free then it will be lost. It will not be
written automatically when the area becomes free again.
An automatically written cycle data is formatted exactly the same way as if the fieldbus master had used
the CMD to request it. That is, in addition to the result data, the STS, SEQ, and LEN fields are also
properly assigned.
After reading automatically loaded data the fieldbus master do not need to indicate that he is done
reading by writing zero (0) to the CMD word.
All normal Process Data functions over the fieldbus are supported in parallel. This means that the fieldbus
master may request Events, Traces as well as Cycle Data's (from the FIFO queue) if so wanted. However,
the master must be aware of that doing so may interfere with the automatic loading of Cycle Data.
Typically the master should issue such commands only in-between cycles and after the last generated
Cycle Data have been read.
Note 1: It is only the first package of a cycle data that is written automatically to the board. This means
that if the cycle data is bigger then the Process data output area, i.e. Data bytes Out, then the
client must request the remaining packages by using normal read request. See chapter: Process
data for a description detailed description of how a cycle data is divided in packages.
Note 2: When using Load Cycle Data automatically the fieldbus master must ensure that it is done
reading data before starting a new cycle.
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