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1MRS755014
6.4.
Profibus-DPV1/SPA Gateway
Installation and Commissioning Manual
Bit
7 6 5 4 3 2 1 0
Momentary
Value +
Event Value
Fig. 6.3.-1 SPA protocol events structure
When the gateway goes on-line, the momentary value of a parameter is read into the
low nibble of the digital input. After this, the momentary value is updated when a
SPA protocol event is generated in the protection relay. This means that the Profibus
master always will have a valid momentary value for the parameter in question.
If the data is not updated based on events, it is possible to lose
information, if a very fast double transition occurs between two SPA
poll cycles. If events are used, then all transitions are catched, but
they may be
It is probable that the loss of a fast double transition is related to the speed of
Profibus DP. The faster the Profibus DP master polls its slaves, the less likely it is
that a double transition is lost.
The events that are supported in the standard configuration templates are listed in
the SPA code column of the cyclic signal table, directly after the SPA code that
provides the gateway with the initial momentary value.
Using indirect SPA messages
It is only possible to use indirect SPA messages in Profibus DP masters that support
Profibus DP version 1 or higher. The master must also be able to address a specific
slot and index. Some masters may require special configuration to meet the
requirements when using indirect SPA messages. It is the acyclic property defined
for version 1 that enables this kind of functionality. Because the indirect SPA
messages are not connected to any poll cycle, they can be used to define own SPA
messages that can be read or written any time by the Profibus DP version 1 master
configuration.
Typical SPA messages are defined for some of the configurations. Nothing prevents
the user from adding new, changing existing or even removing SPA messages from
the configuration. Therefore, the indirect SPA messages defined in the
configurations shall be considered to be a best guess of what might be needed when
using that particular configuration.
Indirect SPA messages are defined using the PCT, see Section 5.4.8.6. Indirect SPA
Messages. In the PCT, the indirect SPA message gets an index that is later used to
refer to that specific parameter. A maximum of 127 messages can be defined.
Events_a
delayed.
SPA-ZC 302
53
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