ADC setting for evaluating frequency response

i am injecting a variable frequency sine thorugh ADC. The reason is to achive open loop frequecny response. i added small perturabtion to steady state phase shift and achieving the resultant output voltage. However, i am confused about ADC trigger as Antonion said to have some Compare B value and set accordingly. i am attaching the pciture of the ADC and alsp Matlab file as well.