ECE 4760: Homework 3

1. The keypad scanning routine given in Lab 3 uses a scheme where the upper and lower nibbles of an i/o register are alternately used for input and output. Figure out a way to scan a 4x4 keypad which drives the vertical wires as 4 output bits and reads the horizontal wires as inputs, with no i/o swapping. Does either scheme have an advantage?
2. Discuss how you will implement the required day:hrs:min clock. The scheme must be as accurate as the crystal.
3. How accurate is the crystal? Find a data sheet.