Are you using CY8CKIT-050 or CY8CKIT-059 ? I assume that you are using CY8CKIT-050 and will provide the answer based on that. Pin 15 is connected to 24 MHz crystal in the corresponding kit. Please see the pin assignment table in the kit user guide . Additionally even though you are using the same device, the kit might have some other feature in hardware. So you have to choose the right pins for each purpose. If you are interested in seeing the TIA output, manually assign it to pins which are visible in the GPIO headers.