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| Example: |
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| The following fragment is part of a Map Descriptor definition; some parameters have been omitted for the purposes of clarity. |
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| Map_Descriptors, |
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| Data_Array_Name, | Data_Array_Offset, | Event Type, | Point Type, | Relay/Loop/Zone Number, | Address, | Length, | Clear_on_Reset, | DA_Bit_Name |
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| DA_MODU | , | 0, |
| ANY, | Module, | 1, | 1, | 99, | Yes, | DB_MODU |
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| DA_MODU_A, |
| 0, |
| ALARM, | Module, | 1, | 1, | 99, | Yes, | DB_MODU_A |
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| DA_MODU_F, |
| 0, |
| FAULT, | Module, | 1, | 1, | 99, | Yes, | DB_MODU_F |
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| DA_MODU_T, |
| 0, |
| TROUBLE, | Module, | 1, | 1, | 99, | Yes, | DB_MODU_T |
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| DA_MPODU_O, | 0, |
| OTHER, | Module, | 1, | 1, | 99, | Yes, | DB_MODU_O |
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| Message = “FAULT: | AC Power | E3 |
| 0:00:04 1/01/92” |
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•This message does not report the status of a Zone, Relay, Loop, Sensor or Module and is therefore assumed to be a panel message. Since there is no Map Descriptor with “Point Type” Panel, the message is ignored.
Message = “TROUBLE: | QZUb L1M22 << Chief's Office >> | 5:24:00 3/03/93” |
•This message reports status for Loop 1 Module 22. Since all the MD’s in the example have a ‘Point Type’=‘Module’, they are all considered for storage.
•The driver looks in the Event Table and finds it has an index value of 34 and a category of 4 (Trouble). Only the MD’s with “Event Type” set to “Any” and “Trouble” are now considered.
•Since the value of the ‘Relay/Loop/Zone’ parameter matches the Loop number in the message, these MD’s remain in contention.
•The Module number of 22 is compared with the MD’s Address and Length Parameters. The Address is the starting number and the length defines the range. Both Map Descriptors have addresses of 1 and length of 99 and thus both are still selected because the Module of 22 falls in this range.
•The driver calculates an offset based on the offset specified in the Map Descriptor and the Module number relative to the Map Descriptor address:
Map Descriptor Offset = 0 Map Descriptor Address = 1 Message Module = 22
Module 1’s data is stored at offset 0 and hence Module 22’s data will be stored at offset 21. The driver stores the value 34 at offset 21 overwriting any data previously stored at that location. This is ‘Index Value’ Storage.
•Secondary storage has been defined using the ‘DA_Bit_Name’ Data Array. The driver doubles the offset as two locations are used for each
address. The driver then reads the value found in the Data_Array, modifies it and writes it back. Since the index value is 34 the driver modifies the 34th bit – or expressed another way, the driver modifies the 2nd bit
•Thus, the driver calculates the offset for Bit Storage as 2 x 21 = 42. The driver sees that bit 34 is 2 2nd bit in the next offset and so the driver reads DB_MODU:43, modifies the value by setting the 2nd bit on and then writing the modified value back. During the modification all other bits are left intact. Thus using the Bit Storage method, a single Module (or sensor…) can keep track of multiple events.
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