Driver Manual
4.4.7Map Descriptor: Example 2 – Writing a Set-Point .
A Data Aire device cannot be written to until it has been read. This is a limitation of the Data Aire protocol. This means that you configuration cannot consist only of wrbc map descriptors. It should consist of a at least a map descriptor like example 1for every unit that you wish to write to.
Map_Descriptor_Name, Data_Array_Name, Data_Array_Offset, Function, node_name, Address, Length, DA_Field , Scan_Interval
Write_SP_01 | , DA_SETPOINTS , 0 | , wrbc , unit1 | , 0 | , 1 | , nom_h_setpt, 120.0s |
The setpoint is | Always leave the |
obtained from this data | address set to zero and |
array. | the length as one. |
Reccomendation
Specify the data field you wish to write.
Pick from table 4.5.1. Ensure that the keyword can be written to the unit type identified as unit1.
Example. If unit1 is a Chiller then the above map descriptor will not function correctly as it can only be used to write to unit types 7,9,14,15.
This is how often the data will be written to the device.
Slow the scan interval down. The dart will only take control of the devices when the network has been idle for at least 50 seconds. If you generate polls too often then the dart will never exercise control.
Use wrbx instead of wrbc. This causes the driver to generate the command message only when the setpoint changes which in turn minimizes communications. Using this method the DART’s control mode is interrupted the least.
FieldServer Technologies 1991 Tarob Court, Milpitas, California 95035 (408)
Visit our website: www.fieldserver.com
Page 19
