Pre-class Assignment

Complete the participation activities in sections 4.1 and 4.2 (you do not need to do the blue challenge activities). Start working on lab 1 (help is available during lab Weds.)

Announcements

• Lab 1 is out and will be due next Tuesday Feb 7
  • I have a conflict with lab hours Weds. Feb 1, so I will have lab hours 2pm-4pm Fri. Feb 3 in Singer 221. You can also schedule office hours with me or post on Ed.
• Office hours: by appointment (email me if none of those times work)

Learning Objectives and Outcomes

In this lecture you will:

• listen to a lecture about how to configure GPIOs using individual pins and using busses in Mbed OS and manipulate bits using bitwise manipulation, and apply that knowledge to reading key presses on a 4 x 4 matrix membrane key pad

By the end of this lecture you should be able to:

• Complete exercises 4 and 5 on the lab

Lecture Content

• Introduction to key pad
• GPIOs
  • DigitalIn, DigitalOut
  • BusIn, BusOut
  • See code examples from class
• Programming the keypad
  • Setup
    • Set up each row as an input with pullup
    • Set up each column as an output
  • Set column one low.
    • Check each row. If the row is low, return button press.
  • Repeat until all columns have been tested.
• Practice: bitwise manipulation
  • Challenge activities 4.2.1, 4.2.2
  • Example bitwise manipulation use cases:
    • key pad
    • getting a digit (0 to 9)
    • converting from upper case to lower case in ASCII (and vice versa)
• Bitwise manipulation cheat sheet. To perform an operation on the nth bit for a variable named test:
  • test bit n: test & (1 << n)
  • set bit n: test |= (1 << n);
  • clear bit n: test &= ~(1 << n);
  • toggle bit n: test ^= (1 << n);

Example codes

#include "mbed.h"

DigitalIn row1(ARDUINO_UNO_D2,PullUp);
DigitalIn row2(ARDUINO_UNO_D3,PullUp);
DigitalIn row3(ARDUINO_UNO_D4,PullUp);
DigitalIn row4(ARDUINO_UNO_D5,PullUp);

DigitalOut col1(ARDUINO_UNO_D6);

int main() {
		col1 = 1;

    // wait indefinitely for keypress
    while (1){
        col1 = 0;
        if (!row1){
            printf("1");
        }
        else if (!row2){
            printf("4");
        }
        else if (!row3){
            printf("7");
        }
        else if (!row4){
            printf("*");
        }
		}
}