User`s guide

Operation Theory • 35
Middle-Trigger Acquisition
Use middle-trigger acquisition in applications where you want 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 users can get (M+N) scans of data under mid-
dle-trigger mode. However, if M_enable is set to 0, the trigger signal will be
accepted at any time. Fig 16 shows the acquisition timing with
M_enable=1.
(M_Counter=M=3, NumChan_Counter=4, PSC_Counter=N=1)
Acquisition_in_progress
Scan_start
AD_conversion
Scan_in_progress
(SSHOUT)(pin8 on CN2)
Aquired data
Acquired & stored data
(M+N scans)
Operation 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 Fig 17.