ADLINK DAQe-2006 - Manual (Page 51)

Operation Theory 39
When the trigger signal occurs before the first M scans of data are
converted, the amount of stored data could be fewer than the orig-
inally specified amount M_counter, as illustrated in Figure 4-6.
This situation can be avoided by setting M_enable. If M_enable is
set to 1, the trigger signal will be ignored until the first M scans of
data are converted, and it assures the user M scans of data under
pre-trigger mode, as illustrated in Figure 4-7. However, if
M_enable is set to 0, the trigger signal will be accepted any time,
as shown in Figure 4-6. Note that the total amount of stored data
will always be equal to the number in the M_counter because data
acquisition does not stop until a scan is completed.
Figure 4-6: Pre-trigger with M_enable=0