High and low level trigger

The analogue trigger input is continuously sampled at the selected sample rate. If the user programmed level is exceeded by the trigger signal then the trigger is seen as valid and acted upon. During recording further triggers are ignored until the recording period has completed. Note that this trigger mode can be combined with AND or OR logic from other sources, e.g. a software trigger (such as key press), the connector dedicated to a TTL trigger input, or analogue signal channel (not to be confused with the analogue trigger input this "analogue signal channel" is where the signal for recording enters). The green trace shows when this high level trigger will be valid for logic combination. A programmed level is simply made by the programmer in the appropriate register of the driver software.
This level trigger also works for low level situations, that is when the trigger signals falls below the programmed level.
Note that in both diagrams above the "START" indicates the point at which the card was started ready to receive triggers, here the start occurred when the trigger condition was already fulfilled, so instantly the card starts to record. The "start" could be at any point in time as determined by the user and his application.