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6.5.4
Message Overload
It can happen that a large number of ALARM_S messages are issued within a
short space of time. This can result in the build–up of processing backlogs.
Communication
If the time gap between the first occurrence of a message and a subsequent
Overload
occurrence is very short, it may be that the first message has not yet even been
sent. In that case, the CPU reports the current status, i.e. the most recent occur-
rence of the message. Every station, i.e. including the operating unit, is in-
formed at the same time, however, that at least one signal change that could not
be sent has occurred.
The message number appears on the operating unit in inverted type (light let-
ters on dark background) if multiple arrivals and departures of the message
have not been able to be recorded.
Figure 6-7 Multiple Arrivals and Departures Could Not Be Recorded
CPU Memory
If there are more messages pending than the CPU can process, any new mes-
Overload
sages are discarded. Only when a message has been fully processed can a new
message be processed.
The date and time of a message appear on the operating unit in inverted type
(light letters on dark background) if it is the last message that could be ac-
cepted by the CPU message buffer.
Figure 6-8 Last Message Accepted by the CPU
Operating Unit
An operating unit can process a maximum of approx. 200 simultaneously
Overload
pending messages (total number of event and alarm messages). If the operating
unit then receives more messages from the CPUs on the network, they can no
longer be displayed. A system message to that effect is then displayed on the
operating unit.
The maximum number of messages that could theoretically be simultaneously
pending on an operating unit is calculated from the sum of the maximum num-
bers possible on the connected CPUs.
TP27, TP37 Equipment Manual
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