ADLINK cPCI-9116 - Manual (Page 51)

Operation Theory
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When an external 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 of DIV_counter * M_counter, as illustrated in fig 12. 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 of obtaining M scans of data under pre-trigger mode, as
illustrated in fig 13. However, if M_enable is set to 0, the trigger signal will be
accepted in any time, as illustrated in fig 12. Note that the total amount of
stored data is still always a multiple of DIV_counter (number of samples per
scan) because the data acquisition won’t stop until a scan is completed.
Acquisition_in_progress
Scan_start
AD_conversion
Scan_in_progress
(SSH_OUT)(pin47)
(M_Counter = M = 3, DIV_Counter=4, SC_Counter=0)
Acquired & stored data
(2 scans)
Operation start
ExtTrg(pin46)
Figure 12: Pre-trigger with M_enable = 0 (trigger occurs before M scans)