The use of an external hardware trigger using Digital Signal source is specified by setting the "TriggerType" property to "HWDigital". When doing so, the condition which initiates the data acquisition is controlled by the "TriggerCondition" property. For National Instruments boards, this value is by default set to "NegativeEdge" i.e. the trigger occurs when the negative (falling) edge of a digital signal is detected.
In the code snippet above, only a rising edge occurs when you write a value "1" to the DIGITALIO line. Hence, as no trigger is received, no data will be acquired which results in the call to the GETDATA function timing out.
To ensure that data has been acquired, you can use one of the following methods:
1. Set the "TriggerCondition" property to "PositiveEdge" or
2. Generate a negative edge on the trigger signal by using the following code snippet:
putvalue(dio, 1);
start([ai ao]);
putvalue(dio, 0);
