The simplest way to synchronize external stimulation with the microscope data collection is for the user to generate a TTL signal that is HIGH when the stimulus is on and LOW when it is off.
This signal should be split and connected to the TTL1 input of Scanbox and the AUX1 input of the Alazartech card (see diagram below). This has TTL-compliant signal (do not use 3.3V boards).
The TTL1 input in the Scanbox allows the system to time-stamp the rising and falling edges of the stimulus TTL signal with the frame and time on which it occurred. The input to AUX1 allows the system to display stimulus markers in real time on top of the traces and save a log of the TTL data along with the real time traces.
If you are using only TTL1, please use imask=2 in your configuration file. If you are using both TTL1 and TTL0 use imask=3 in the configuration file. Never enable a TTL event input without having something connected there.
More information here.