We managed to successfully apply frame rate control via external trigger from a pulse generator.
We supplied 5V pulse train when connected to the optocoupler load, and connected to pins 1 and 2 of external trigger (on the frame grabber board) for using camera 0 (which is the case for us).
Then made the following changes to the config file dalsa_1m60.cfg;
MODE_CNTL_NORM: A0 (previously this value would have been 00)
user_timeout: 0 (this line should be added)
Then I saved the new config file as dalsa_1m60_et.cfg
Next, I loaded the new config using initcam command, then set the exposure mode to be 3. This can be done either using serial_cmd directly or using HS_Camera method set_exposure_mode.
In exposure mode 3, the exposure time is set by the time separation between the falling edges of the pulses, and the camera sets the expousure time to be the maximum value possible (as specified in the camera manual).
Then I took 10 images using take command, and verified that the frame rate is equal to the frequency of the pulse. We tested 1 Hz and 2 Hz pulse trains, and the frame grabber recoded 1 frames per sec and 2 frames per sec respectively.
We could not yet test the frequency values < 1 Hz as pulse generator we used could not go under 1 Hz.
We used another pulse generator to test pulse frequencies under 1 Hz, and verified that external trigger mode still works.