This project uses 2 Atmega16 with 16 MHz external clock. The first microcontroller is used to capture inputs from keypad 4 x 4. The second microcontroller is used to show outputs on LCD HD44780 2 x 16. I use asynchronous mode for this project.
This is the schematic:
But if you want to use synchronous mode, PINB.0 of first AVR should be connected to PINB.0 of second AVR.
This is the sample of this project that I have made.
If you want to know how to connect AVR with LCD HD44780, see my other post here.