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Multiprocessor Communication
10.2.4
How the Buffer is
Processed and Managed
Principle
Data protection
Management
10 - 18
The buffer is based on the FIFO principle (first in - first out, queue
principle). The data is received in the order in which it is sent. This
applies to each individual link (identified by the transmitting and
receiving CPU) and is independent of other links.
The buffer is battery-backed; this means that the "automatic warm
restart following a power down" is possible without any restrictions. A
loss of power during a data transfer does not cause any loss of data in
the programmable controller.
The coordinator 923 C has a memory capacity of 48 data fields each
with a fixed length of 32 words. The INITIALIZE function assigns
these fields to individual CPU links.
Each memory field can receive exactly one field of data. The length
of the data can be from 1 data word to 32 data words. A data field is
entered in a memory field by a SEND function and read out again by a
RECEIVE function.
The number of memory fields assigned to a link is directly related to the
parameters for the transmitting capacity (SEND, SEND TEST function)
and receiving capacity (RECEIVE, RECEIVE TEST function).
The transmitting capacity indicates how many of the memory fields
reserved for a link are free at any particular time.
The receiving capacity indicates how many of the memory fields
reserved for a link are occupied at any particular time.
The sum of the transmitting and receiving capacity is always equal to
the number of memory fields reserved for a link.
CPU 948 Programming Guide
C79000-G8576-C848-04
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