Data processor with a hardware keyscan circuit, hardware keyscan circuit, and method therefor

摘要

A data processor (50) includes a hardware keyscan circuit (54) to interface to an external keypad matrix (80). In one embodiment, the data processor (50) has a first register (62) for driving data to rows of the keypad matrix (80), and a second register (63) for inputting signals from columns of the keypad matrix (80). A set of weak pullup elements (71) connected to the columns is always conductive. A set of strong pullup elements (75) connected to the columns is conductive only after the hardware keyscan circuit (54) detects that a key (89) is depressed and disables the driving of the rows. Thus, pullup time and power consumption are minimized. The hardware keyscan circuit (54) also includes a data direction register (61) which has a shift control input terminal so that in response to a local state machine (64), the data direction register (61) acts as a shift register to sense the row with the depressed key (89), without intervention from a central processing unit (51).