User`s guide

Operation Theory • 33
Note that if a trigger event occurs when a scan is in progress, the data
acquisition won’t stop until the scan completes, and the stored M scans of
data includes the last scan. Therefore, the first stored data will always
be the first channel entry of a scan (that is, the first channel entry in
the Channel Gain Queue if the number of entries in the Channel Gain
Queue is equivalent to the value of NumChan_counter), no matter when a
trigger signal occurs, as illustrated in Fig 13, where M_counter = M =3,
NumChan_counter = 4, PSC_counter = 0.
Acquisition_in_progress
Scan_start
AD_conversion
Scan_in_progress
(SSHOUT)(pin8 on CN2)
(M_counter = M = 3, NumChan_counter =4, PSC_counter=0)
Aquired data
Acquired & stored data
(M scans)
Operation start
Trigger
Data acquisition
won’t stop until a
scan completes
Trigger occurs
Figure 13: Pre-trigger (trigger with scan is in progress)
When a trigger signal occurs before the first M scans of data are converted,
the amount of stored data could be fewer than the originally specified
amount in NumChan_counter * M_counter, as illustrated in fig 14. 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 user can get M scans of data under pre-trigger mode, as
illustrated in fig 4.1.5. However, if M_enable is set to 0, the trigger signal
will be accepted in any time, as illustrated in fig 15. Note that the total
amount of stored data is still always a multiple of NumChan_counter
(number of samples per scan) because the data acquisition won’t stop until
a scan is completed.