Selecting analog input channels 8 through 15, and 24 through 31 for ADC conversion is not supported due to a defect in the ADC driver. The problem is reproducible on FM0+ and FM4 family of devices when using the ADC driver from Peripheral Driver Library (PDL) 2.1.0. Is there a workaround?
No. The problem will be corrected in the next PDL 2.x release. Contact Cypress technical support (http://www.cypress.com/mycases) for possible firmware updates and help with using the specified channels in ADC conversion.