Measurement Computing DAQFlex User Guide - Manual (Page 20)

DAQFlex Software User's Guide Using DAQFlex Software
20
ReadScanData() parameters
 The first parameter to the ReadScanData method is the number of samples to read.
 The second parameter is a time out value in milli-seconds. A value of 0 indicates no timeout
specified.
The ReadScanData method is synchronous, and will return when the number of requested samples are
available for reading. When the number of requested samples are available, the DAQFlex software
copies the requested number of samples from an internal buffer to a new array of data. The DAQFlex
software keeps track of the buffer index so that multiple calls to ReadScanData always return
contiguous data.
Internal buffer
An alternative method for reading scan data is to enable a user-defined callback method. When you
enable a callback method, the DAQFlex software invokes your user-defined method when a specified
number of samples are available for reading, when a scan completes, or if a scan error occurs. This is
done using the EnableCallback method as shown below:
C#
Device.EnableCallback(callbackMethod, callbackType, callbackCount);
VB
Device.EnableCallback(Addressof CallbackMethod, CallbackType, CallbackCount)
The callbackMethod is the name of the method that will be invoked by the DAQFlex software. The
callbackMethod is a class method that must have the following form:
C#
void CallbackMethod(ErrorCodes errorCode, CallbackType callbackType, object callbackData)
VB
Sub CallbackMethod(ByVal errorCode As ErrorCodes, ByVal callbackType As CallbackType,
_ ByVal callbackData As Object)
The callbackType is an enumeration that defines when the callback method will be invoked.
CallbackType
Member Name Description
OnDataAvailable Specifies that the callback method will be invoked when a specified
number of samples becomes available for reading.
OnInputScanComplete Specifies that the callback method will be invoked when a finite scan has
complete or when a continuous scan is stopped.
OnInputScanError Specifies that the callback method will be invoked when an input scan
error occurs.
Only one callback method can be specified for each callback type. When the callback type is set to
OnDataAvailable, set the callbackData parameter to the number of samples you wish to receive in the
callback method. When the callback type is set to OnInputScanComplete or OnInputScanError, set the
callbackData parameter to null or Nothing.