ECE 4760: Homework 2

1. Draw the lowpass circuit required in Lab 2 to filter the PWM output.
   Specify R and C to meet the requirements stated in the first paragraph of the Procedure section of the lab writeup.
2. What is the maximum frequency of sine wave you can generate on the Mega644 using the fastest PWM mode?
   Assume a hardware clock frequency of 16MHz and that you will change PWM values every PWM cycle.
   Assume also that you require 8 samples/sinewave cycle to produce a filterable signal.
3. The keypad scanning routine given in Lab 2 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?
4. How accurate is the crystal? Find a data sheet.
   Does the crystal accuracy limit the measured accuracy on the oscilloscope? Justify your answer.