29.5.2 I/O Lines

The pins used for interfacing the PTC may be multiplexed with GPIO lines. When the PTC subsystem is activated and the X-Y lines selected, the GPIO switches automatically to analog state. The ADC modules possibly hanging on the same PTC analog lines should not use the same GPIO for ADC conversion. Adjacent GPIO lines to PTC lines must not be used to output high speed signals to avoid crosstalk with PTC sensing.

When a line is disabled, the corresponding I/O pin is not reserved for the PTC subsystem, and it can be used for some alternative I/O function.

There is an individual selection bit for each Y or X line. In normal cases, just one line should be active at the same time. For more advanced uses, like proximity sensing, several lines may be selected in parallel. The input and output functionality, such as charging and sensing pulses of the selected line, is controlled automatically by the PTC digital controller sequencer in various operating modes. The I/O lines used for analog PTC_X lines and PTC_Y lines must be connected to external capacitive touch sensor electrodes. External components are not required for normal operation.