ADLINK cPCI-9116 - Manual (Page 52)

42
• Operation Theory
Acquisition_in_progress
Scan_start
AD_conversion
Scan_in_progress
(SSH_OUT)(pin47)
(M_counter = M = 3, DIV_counter=4, SC_counter=0)
Aquired data
Acquired & stored data
(M scans)
Trigger signals which occur in the shadow
region(the first M scans) will be ignored
Operation start
ExtTrg(pin46)
The first M scans
Figure 13: Pre-trigger with M_enable = 1
Note: The SC_counter must be set to 0 in pre-trigger acquisition mode.
Middle-Trigger Acquisition
Use middle-trigger acquisition in applications where you want to collect data
before and after an external trigger event. The number of scans stored before
the trigger is specified in M_counter, while the number of scans after the trigger
is specified in SC_counter.
Like pre-trigger mode, the number of stored data can be less than the specified
amount of data (DIV_counter *(M_counter+SC_counter)) if an external trigger
occurs before M scans of data is converted. The M_enable bit in middle-trigger
mode takes the same effect as in pre-trigger mode. If M_enable is set to 1, the
tigger signal will be ignored until the first M scans of data are converted, this
assures user of obtaining 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.
Fig 14 shows the acquisition timing with M_enable=1.