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Driver Data_Type |
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|
MN2_Type values |
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Point Type | Known Value2 | Suggested Value3 |
AI | 1 |
|
AO | 2 |
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BI | 3 |
|
BO | 4 |
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ADF |
| 5 |
ADI |
| 6 |
BD |
| 7 |
If a large number of points are to be monitored, optimal efficiency is achieved by using the COS mechanism instead of reading each individual point directly. An N2Open device responds to a COS poll with a change record if a change has taken place. On startup the device will report the state of all its points when it receives a COS poll.
Three kinds of Map Descriptors are required for every node that is to be monitored using COS:
•A COS initialization Map Descriptor with Function set to ARS and MN2_Function set to COS_Enable. This Map Descriptor enables COS polling of those points on the VMA for which Passive Map Descriptors exist.
•A COS polling Map Descriptor with Function set to rdbc and MN2_Function set to COS.
•A Passive (i.e. Function set to Passive) Map Descriptor for every point on that node that is to be monitored. Any COS records received will be stored to the matching Map Descriptor data location.
See example in Section 4.4.5
Using Override and Release - VMA
It is normally not necessary to use the Override command explicitly as the FieldServer automatically uses this command when the Current Value attribute of a point is written. For any other attribute it uses the Write command. It will sometimes be necessary to send a Release command to an overridden point, however. To do this, a Map Descriptor must be configured with Function set to wrbx and MN2_Function set to Release. Then, when any value is stored to the Map Descriptor data location, the Release command will be sent to the VMA point specified by the Map Descriptor.
Note: The VMA Release function only works for analog and binary inputs (AI and BI). Outputs may be restored to their original value using an explicit write command.
2For information only. Do not use Driver type for these, but specify AI, AO, BI or BO directly in the Data_Type field.
3These values are believed to be correct for the corresponding point types, but no guarantee can be given at this time.
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