ProSoft Technology PS-QS-1x10-0781 - Manual (Page 40)

FieldServer Configuration Manual Page 40 of 90
FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web: www.fieldserver.com
Tel: (408) 262-2299 Fax: (408) 262-2269 Toll Free: (888) 509-1970 email: [email protected]
5.6.3 Limitations and Operational Considerations

Each Data Array location to be preloaded requires its own preload line in the configuration file.

The value specified must be compatible with the format of the Data Array – e.g. Integer arrays cannot be
preloaded with numbers that contain fractions.

Preloads cause Data Array updates. The FieldServer kernel does not differentiate between an update on a
Data Array performed as a preload or as the result of a store after processing a protocol message. If the
Data Array point is associated with a Map Descriptor using the Write-on-update (Wrbx) function or an
Rdbx function set to “Write through”, the preload will trigger the write. Refer to Section 4.3.3 for more
information.

The ‘Preload_Data_Format’ must not be confused with the format of the Data Array being preloaded.
The ‘Preload_Data_Format’ tells the kernel how to interpret the number specified by the
‘Preload_Data_Value’ parameter. Example: If ‘Preload_Data_Format’ is set to Byte then the preload value
is cast to a byte* before being stored in the Data Array.
5.6.4 Example 1 – Load a Value
Preloads
Data_Array_Name , Preload_Data_Value , Preload_Data_Format , Preload_Data_Index
DA_SDA1
, 11 , - , 0
Note: If the format of the Target Data Array is “Bit”, then the value 11 will not be stored as Bit arrays can only
store 1 and 0.
5.6.5 Example 2 – Load a Value – Effect of Target Data Array Format
Data_Arrays
Data_Array_Name , Data_Format , Data_Array_Length
DA_1
, FLOAT , 20
DA_2 , BYTE , 20
Preloads
Data_Array_Name , Preload_Data_Value , Preload_Data_Format , Preload_Data_Index
DA_1
, 257 , FLOAT , 0
DA_2 , 257 , FLOAT , 0
The Data Array named ‘DA_SDA1’
must have been previously defined in
the configuration file or else there
will be a configuration error. Format specified with a dash, therefore the value
11 will be type cast to an unsigned 32-bit integer.
Omitting the value altogether would have the
same effect.
The value 257 is cast to a
floating point number.
The value 257 will be stored
Only numbers in the range 0-255 inclusive
can be stored in a BYTE array. The kernel
chops off the part of the number that
exceeds the byte. Therefore the value stored
will be 1.