ADC continuous mode and start-stop mode

Hello,
I implemented motor control system using F28335 DSP. I'm having issues with the sampling rate of the ADC output.

In order to test the ADC, I created a simple model (ADC_test.psimsch). PWM switching frequency is 10k. It works fine when ADC mode is continuous. But when I set it to start-stop(8 channel) the sampling rate of the ADC out put is 4 times slow. When start-stop(16 channel) mode is selected, the sampling rate is 8 times slow. Can you please help me to solve this issue. I need to use start-stop(16 channel) for my drive.

Thank you.