2-12
Functional Description
Triggers
A trigger is an event that must occur before a DAS-800 Series board starts
an analog input operation. You can use one of the following trigger
sources to trigger an analog input operation:
●
Software - When you start the analog input operation, conversions
begin immediately.
●
Hardware - You connect a digital trigger signal to the digital input
IP1 / TRIG pin (pin 25) of the main I/O connector. The trigger event
occurs when the board detects a rising edge on IP1 / TRIG.
The actual point at which conversions begin depends on whether you
are using an internal or external clock source. These considerations
are described as follows:
–
Internal clock source - The 8254 counter/timer circuitry remains
idle until the trigger event occurs. When the trigger event occurs,
the board initiates the first conversion immediately.
–
External clock source - Conversions are armed when the trigger
event occurs. At the next falling edge of the external clock source,
the board initiates the first conversion.