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4.4.4.Map Descriptor Example 1 – Read a Table
This example illustrates how to read the entire contents of a table called ‘DISPLAY’. The Map Descriptor is connected to a node using the node name and a node definition provides a connection to a port. Thus this Map Descriptor is connected to a port via its node. The FieldServer will use that port to send this poll which will be generated every 5 seconds.
The value extracted from the response will be stored in the array called DA_DISPLAY. Ensure that it is suitable format for storing a number – FLOAT is suggested. The driver stores the value of the 1st element at offset 1; the 2nd element at offset 2… The number of table elements whose values have been successfully stored at is stored at offset zero.
//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, | Length, | Scan_Interval, | Table_Name, | Field_Name | |||
Read_Table_Md | , | DA_DISPLAY , | 0 | , | rdbc , | FAN01 , | 100 , | 5.0s | , | DISPLAY , | EVERYTHING |
Responses are stored in this data array. Table element x gets stored at offset x, where x is a non- zero integer.
Offset zero is used by the driver to report how many values were stored.
The driver generates a read poll continuously.
The node name connects the Map Descriptor to a node definition.
The length is set to a number big enough to contain all the table’s variables.
The name of the table to be read.
By using the keyword ‘EVERYTHING’ you are telling the driver to read the whole table.
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