User`s guide

32
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Operation Theory
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 set of 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 Figure 13, where
M_counter = M =3, NumChan_counter = 4, PSC_counter = 0.
A
cquisition_in_progress
Scan_start
A
D_conversion
Scan_in_progress
(SSHOUT)(pin8 on CN2)
(M_counter = M = 3, NumChan_counter =4, PSC_counter=0)
Aq
uired data
A
cquired & stored data
(M scans)
O
p
eration start
Trigger
Data acquisition
won’t stop until a
scan completes
Tri
gg
er occurs
Figure 13: Pre-trigger (trigger with scan is in progress)
When a trigger signal occurs before the first M scans are converted, the
amount of stored data could be fewer than the originally specified amount
in NumChan_counter * M_counter, as illustrated in Figure 14. This situa-
tion 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 that users can get M scans of data under pre-trigger mode,
as illustrated in Figure 15. However, if
M_enable
is set to 0, the trigger
signal will be accepted in any time, as illustrated in Figure 14. 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.