From Bob Rau Consulting:
1 Wire Keyboard Calculator is a tool for embedded system designers to implement a keypad using a single analog to digital converter (A/D) input. For larger keyboards, or keypads that require chording (more than one key pressed at a time) multiple A/D inputs can be used, each with a portion of your complete keypad. Two to 64 key keyboards are supported, however keyboards beyond 26 keys may be hard to realize. 1-Wire keyboards offer lower EMI than scanned keyboards, and need fewer ESD protection components to implement, and require just 1 pin on a microcontroller. The user enters the keypad matrix size, the A/D specifications, the resistor specifications, and the environmental requirements.