Siemens CPU 948, Programming Manual

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Summary Buffering data on the coordinator COR 923C allows the asynchronous
operation of transmitting and receiving CPUs and compensates for
their different processing speeds.
Since the capacity of the buffer is limited, the receiver should check
"often" and "regularly" whether there are data in the buffer (RECEIVE
TEST function, receiving capacity > 0) and should attempt to fetch
stored data (RECEIVE function). Ideally, the RECEIVE function
should be repeated until the receiving capacity is zero. This means that
the transmitted data are not buffered for a longer period of time and
that the receiver always has the current data. This also means that
memory fields remain free (the transmitting capacity is increased) and
prevents the sender from being blocked (i.e. when the transmitting
capacity is zero).
Note
A receiving capacity of zero represents the ideal state (i.e. all
transmitted data have been fetched by the receiver), on the other
hand a transmitting capacity of zero indicates incorrect planning,
as follows:
- the SEND function is called too often,
- the RECEIVE function is not called often enough
or
- there are not enough memory fields assigned to the link.
The capacity of the buffer is insufficient to compensate tempo-
rary imbalances in the frequency with which the CPUs trans-
mit and receive data.
Multiprocessor Communication
CPU 948 Programming Guide
10 - 20
C79000-G8576-C848-04