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4.6.Map Descriptor Example 2 – Write Hold (or Sample) Times to a Device.
In this example the driver writes the hold time to the field device. The time is specified in seconds. A max of 23 hours 59 minutes and 59 seconds can be specified. To write Sample Times simply change the Met1_Function to ‘Sample Time. The driver extracts the time from the response and stores the hours at the specified offset, the minutes in the next Data Array location and the seconds in the 3rd location.
//Client Side Map Descriptors
Map_Descriptors |
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Map_Descriptor_Name, | Data_Array_Name, | Data_Array_Offset, | Function, | Node_Name | Met1_Function, | Length |
Write_Time, | DA_TIMES, | 0, | WRBX, | MET1, | Hold Time , | 1 |
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The location in the Data Array
The driver will extract the time in seconds from the Data Array specified here and use it to form the command message to the field device.
This function ‘wrbx’ tells the driver to only send the command each time the value found in the specified DA:offset is updated. Update means each time some other protocol writes to this DA:offset
Change | this | to | Tells | the | |
‘Sample | Time’ | to | FieldServer that | ||
command a sample | one | element of | |||
time | or | make two | the data array is | ||
Map | Descriptors | – | reserved for this | ||
each with the correct | Map Descriptor. | ||||
time function. |
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4.7.Map Descriptor Example 3 – Read the operating mode.
In this example the driver reads the operating mode from the field device. The driver stores a single element of data extracted from the response. The driver stores a ‘C’ to indicate the field device is counting, a ‘H’ to indicate the device is holding and an ‘S’ to indicate that it has stopped. If the mode is not recognized the driver store s a ‘?’. If another protocol reads these states from the FieldServer it will probably display the ASCII value corresponding to each mode letter: ‘C’=67 ‘H’=72 and ‘S’=83
//Client Side Map Descriptors
Map_Descriptors |
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Map_Descriptor_Name, | Data_Array_Name, | Data_Array_Offset, | Function, | Node_Name | Met1_Function, | Length, | Scan_Interval |
Write_Time, | DA_MODE, | 0, | rdbc, | MET1, | Mode , | 1, | 1.0s |
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