The actual part number that Yogesh was referring to is the 74C922. Not the 74C992 as you stated Ian. Of course the part 'C922 is pretty much an obsolete part and should only be used in one-up hobbiest, student or experimenter projects. For production projects I would find another solution. The simplest of course is to get a microcontroller that has a configuration with enough I/O pins so that the keypad can connect right at the pins and use a simple keypad scanning algorithm in software. If you are really hard up for I/O pins to support this then consider operating the LCD interface (if it is the bog standard default "hitachi compatible" character mode type controller) in the 4-bit mode. You can then use the gained four port pins to drive the keypad columns and implement a 74xxC125 type buffer to read the keypad row inputs onto the shared 4-bit bus of the LCD controller. You would also need another single port pin to be the keypad read signal that is driven by software in a manner that is mutually exclusive from the read/write cycles to/from the LCD display controller.

Michael Karas