Touch sensor locating mode

A touch-sensitive input device, comprising:

• receive circuitry;
• a capacitive touch sensor having a plurality of portions;
• and
• a controller configured to:
• responsive to not detecting a finger or a pen, operate the touch sensor in a locating mode by successively driving, for a touch frame of the locating mode, each portion of the touch sensor with a fixed DC voltage and multiplexing the portion of the touch sensor to the receive circuitry in a predefined sequence;
• and
• responsive to detecting the pen in the locating mode, operate the touch sensor in a tracking mode by driving, for a touch frame of the tracking mode, a selected portion of the touch sensor with the fixed DC voltage and multiplexing the selected portion to the receive circuitry to track the pen, the selected portion selected based on a detected location of the pen relative to the touch sensor and being varied as the detected location changes in the touch frame of the tracking mode.