User`s guide

34
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Operation Theory
Middle-Trigger Acquisition
Use middle-trigger acquisition in applications to collect data before and
after a trigger event. The number of scans (M) stored before the trigger is
specified by M_counter, while the number of scans (N) after the trigger is
specified by PSC_counter.
Like pre-trigger mode, the number of stored data could be fewer than the
specified amount of data (NumChan_counter *(M+N)) if an external trigger
occurs before M scans of data are converted. The
M_enable
bit in mid-
dle-trigger mode takes the same effect as in pre-trigger mode. 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+N) scans of data under
middle-trigger mode. However, if
M_enable
is set to 0, the trigger signal
will be accepted at any time. Figure 16 shows the acquisition timing with
M_enable=1.
(M_Counter=M=3, NumChan_Counter=4, PSC_Counter=N=1)
A
cquisition_in_progress
Scan_start
A
D_conversion
Scan_in_progress
(
SSHOUT
)(pin8 on CN2)
Aq
uired data
A
cquired & stored data
(M+N scans)
O
p
eration start
Trigger
M scans before
trigger
N scans
after trigger
Trigger signals which occur in the shadow
region(the first M scans) will be ignored
The first M scans
Figure 16: Middle trigger with M_enable = 1
If a trigger event occurs when a scan is in progress, the stored N scans of
data would include this scan.
And the first stored data will always be
the first channel entry of a scan,
as illustrated in Figure 17.