Incorrect ADC Values on Cypress PSoC 3 With Signal Generator Input (1Vpp, 1V Offset)

I am making an oscilloscope using Cypress PSoC 3. The sample data is sent to the computer and plotted. The ADC is used in single ended configuration. Whenever I connect the signal generator to the board, it throws a lot of garbage values to the UART. On the signal generator, the amplitude set is 1Vpp with 1V dc offset at a frequency of 100Hz. The frame received looks something like this $18 18 18 18 18 18 18 18 18 18%. This problem did not occur when I tried connecting a DC power supply. When I read the component data sheet, it mentioned obtaining a 16 bit result for 8 bit resolution to avoid wrap around. When I obtained 16 bit result, I got 277 instead of 18. The peak amplitude applied is 1.5V, so the sample value that should be obtained is 191 or below from the ADC. This problem occurs irrespective of the input waveform, sine, square or triangular. I tried using a different kit and a different function generator. Futile.

The problem is: The ADC does not send proper sample values of the input signal on connecting a signal generator.