I am surprised that you couldn't support this design in one microcontroller. Did you arrange your keypad as a matrix? You can support a 24 key matrix in either a 6x4 or a 5x5 organization. Both configurations require only 10 I/O port pins. A typical character mode LCD module uses signals D4-D7, RW, RS, E for 7 more port pins. That is a total of 17. That leaves a lot of I/O pins left out of the total 32 on a typical 8052.

Scanning a keypad matrix is very easy in 8052 code.

mike karas