Last Revision Date: 6/22/2015
Many of our cameras provide asynchronous trigger functionality, which allows the start of integration (shutter) to be initiated by an external electrical source (hardware trigger) or camera register write (software trigger). All cameras that implement a software asynchronous trigger can be triggered via the SOFTWARE_TRIGGER register 0x62C. (For Dragonfly: SOFT_ASYNC_TRIGGER 0x102C.) See the Digital Camera Register Reference for more information.
The time from when the register is written on the camera to when the start of integration occurs can only be approximated. The average time from register write request to register write response is approximately 49.85µs. The "register write success" response is only sent from the camera to the host system once the internal trigger pulse is initiated. We then add the trigger latency (time from the trigger pulse to the start of integration) to this, which is approximately 6 µs for a 640 x 480 camera. Therefore, the total time from when the register is written to the start of integration is approximately 56 µs.
The important point to note is the above timing is solely from the camera perspective. It is virtually impossible to predict timing from the user perspective due to latencies in the processing of commands on the host PC (i.e., the time from the user hitting a keyboard key to initiate the register write, to the start of integration).