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FS-8700-82 Carrier DataLink Page 11 of 31
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4.4.5. Map Descriptor Example 2 – Read a Variable
This example illustrates how to read single variables from a Carrier Device. A Map Descriptor needs to be defined for each variable.
Reading variables is effective for reading a limited set of variables from a table(s). Scaling can be applied when the driver stores the
value by using the additional parameters: Data_Array_Low_Scale, Data_Array_High_Scale, Device_Low_Scale, Device_High_Scale
Map_Descriptor_Name, Data_Array_Name, Data_Array_Offset, Function,
Node_Name,
Length,
Scan_Interval,
Table_Name,
Field_Name
Read_Temps_Md1 , DA_TEMPS , 0 , rdbc , FAN01 , 1 , 5.0s , DISPLAY , RAT
Read_Temps_Md2 , DA_TEMPS , 1 , rdbc , FAN01 , 1 , 5.0s , DISPLAY , SAT
4.4.6. Map Descriptor Example 3 – Write A Variable
This example illustrates how to force a variable. Always set the length to 1 for a write. If the variable cannot be written then an error
will be reported. In this example the variable being written is called ‘FAN’. It can be set on/off because is a discrete point.
Map_Descriptor_Name, Data_Array_Name, Data_Array_Offset, Function, Node_Name, Length, Scan_Interval, Table_Name, Field_Name
Write_Md1 , DA_DISPLAY , 0 , wrbc , FAN01 , 1 , 5.0s , DISPLAY , FAN
As we are using the same data array for both variables,
we change the offset.
The ‘RAT’ temperature will be stored at index 0 (first
element), the SAT temperature will be stored at index 1
(2
nd
element of array).
If the first element of
this array is set to 1,
the fan will be set ON;
if set to zero the fan
will be set OFF.
The pneumonic variable name.
Space Temperature -40.0 dF RAT
Supply Air Temperature -40.0 dF SAT
The variable names are supplied by the Carrier Corporation. Refer to
Appendix A.2 for assistance in determining version names.
Take care to
specify variables
that can be forced.
This function ensures that the driver
writes the Setpoint to the device
continuously (every 5 seconds in this
example.) Use WRBX to generate a
write message each time the value in
the array is updated.