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Messages
Example:
A CPU 315 can process a maximum of 50 simultaneously pending messages.
Accordingly, an operating unit can handle a maximum of four CPU 315s send-
ing ALARM_S messages without overflow problems occurring.
6.5.5
Updating
Since the CPU stores the message information when a fault occurs, individual
network stations (e.g. an OP) can log on at a later date and obtain an update.
However, the CPU only stores information about pending messages. Once all
events (arrival, departure, acknowledgement) have occurred, the message is
deleted from the CPU.
When obtaining an update, therefore, the operating unit processes any missing
events automatically if a message is not known to the PLC but the arrival and
acknowledgement events are not entered on the operating unit.
The events are not entered in the message buffer in that case, however.
Events processed in this way are identified on the operating unit by displaying
the message status symbols in inverse type thus:
Figure 6-9 Automatically Processed Events
6-22
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TP27, TP37 Equipment Manual
Release 01/00
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