SU640CSX
4110-0462, Rev. B
Page 58 of 97
© 2016 UTC Aerospace Systems
Date Printed: 1-Dec-2016
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In trigger mode 1, the camera uses the external trigger signal to control the frame period while internally
controlling the exposure period. The minimum trigger pulse width for trigger mode 1 is 0.5µs. The
exposure time is set by the operational setting chosen and can be overridden with the EXP command. The
camera detects a trigger transition via the currently selected trigger input to initiate exposure (integration).
If an active high polarity is selected the camera uses a low to high transition. If active low polarity is
selected the camera uses a high to low transition. The delay between this trigger transition and start of
exposure is 5 to 6 pixel periods. (See Section 5.11 for a discussion on determining the pixel clock period.)
The ceiling of the trigger rate for this mode is the maximum frame rate. If the maximum trigger rate is
exceeded, a camera error will be reported as described in Section 5.16.16, yet will not disable the
camera’s ability to acquire on future triggers (an error could mean that the camera is missing triggers).
Note that some frame grabbers have a time-out that can be exceeded while the camera awaits a trigger;
the camera does not time-out. The timing sequence of the camera for trigger mode 1 is shown in the
Figure.
In trigger mode 2, the camera uses the external trigger to both externally set the exposure time and the
frame rate. During this external triggered mode, the camera waits for a trigger pulse before initiating a
scan of the focal plane array. The camera detects a trigger transition via the currently selected trigger
input to initiate the start of exposure (integration). It uses the low to high transition, if an active high
polarity is selected, or the high to low transition, if an active low polarity is selected. A trigger transition
of the opposite polarity ends the exposure. In other words, the active trigger pulse width determines the
exposure time and the trigger frequency determines the frame rate. In trigger mode 2, the delay between
the trigger transition and start of exposure is 3 to 4 pixel clock periods. The delay between the trigger
transition and end of exposure is 3 to 4 pixel clock periods plus 28 pixel clock periods for FPA clocking
overhead, as described in Section 5.11. The timing sequence of the camera for trigger mode 2 is shown in
Figure 15. Trigger mode 1 exposure and readout timing sequence.
