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4.11.Map Descriptor Example 7 – Read the Current Record
In this example the driver reads the current record and stores the values in the specified Data Array. A single record comprises the following data: status; date and time and a count for 1 or more locations. The driver has no advance knowledge of the number of count fields to expect in the response. It simply stores them in consecutive locations in the Data Arrays. To map these counts to an upstream protocol, the order of the count fields must be known. The driver can store a maximum of 20 count fields. The Map Descriptor length must be set to a value that allows for enough data to be stored bearing in mind that it requires 8 DA elements to store the status, date and time and period.
One of these Map Descriptors is required for each device from which the current record is to be read..
// Client Side Map Descriptors |
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Map_Descriptors |
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Map_Descriptor_Name, | Data_Array_Name, | Data_Array_Offset, | Function, | Node_Name | Met1_Function, | Length, | Scan_Interval |
Read Record, | DA_DATA, | 0, | Rdbc, | MET1, | Current Record, | 20, | 1.0s |
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Driver stores the current record information in the Data Array specified here, starting at the specified offset. The data is arranged as follows.
0Status Byte
1 Date - Month
2 Date - Day
3 Date - Year
4 Time - Hours
5 Time - Minutes
6 Time - Seconds
7 Period
8 Count #1
9 Count #2
10 Count #3 …
The length must be set to a value large enough to store the 8 fixed data items and the variable number of count fields.
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