Hitachi HV-D20P Operation Manual page 51

Note: Prohibited period of the external trigger pulse timing
For each external trigger mode, when the end edge of external trigger pulse is input in the prohibited
period (shown in the under figure), the picture is not output after the SYNC reset.
Please input the repetition period of trigger pulse with the following specification, to avoid the trigger
input to an above prohibited period.
The period of the next end edge trigger pulse from the previous end edge of trigger
CCD MODE: FLD, except from nV to nV+2H
CCD MODE: FRM, except from 2nV to 2nV+2H
(V: a vertical synchronous period, n: an integer)
EXTERNAL TRIGGER
CAMERA SYNC
Prohibited period of the end edge of external trigger pulse
(1H period before the start of camera V SYNC)
38
nV
SYNC reset timing
Next SYNC Reset timing