A processing system comprises interface circuitry and a timing controller. The interface circuitry is configured to receive a vertical sync period indicator that indicates a start of an external vertical sync period. The timing controller is configured to, in response to a change in a display frame rate, control timing of a display drive operation and a proximity sensing operation to maintain a proximity sensing frame rate based on input timing of the vertical sync period indicator to the interface circuitry. The processing system is configured to supply drive signals to display elements of a display panel in the display drive operation and acquire sensing signals from sensor electrodes of the display panel in the proximity sensing operation.