National Instruments 653X Manuale Utente

The three types of trigger signals available are the start trigger, the stop 
trigger, or the start and stop trigger.

A start trigger is a trigger that initiates a pattern I/O upon receipt of a 
hardware trigger on the ACK (STARTTRIG) pin.

Figure 2-16.  Starting Data Transfer Using a Trigger

When using a stop trigger, transfer starts upon a software command. Once 
a hardware trigger is received on the STOPTRIG pin, a predetermined 
amount of pretrigger and posttrigger data is saved in the buffer. Once this 
data is in the buffer, transfer stops. If the stop trigger arrives before all the 
pretrigger data is acquired an error will return in software.

Figure 2-17.  Stopping Data Transfer Using a Trigger

When using a start and stop trigger, transfer starts upon receiving a trigger 
on the start trigger line (ACK/STARTTRIG pin) and ends upon receiving 
a trigger on the stop trigger line (STOPTRIG pin) and a predetermined 
amount of pretrigger and posttrigger data is saved in the buffer. If a stop 
trigger is received before a start trigger, it is ignored. If the stop trigger 
arrives before all the pretrigger data is acquired an error will return in 
software.

REQ

ACK (STARTTRIG)

Posttrigger Data

REQ

STOPTRIG

Pretrigger Data

Posttrigger Data