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Question 3: In class we showed how to simply light up an LED on our Teensy microcontroller. In fact, the procedure is similar for all processors including a simpler 8-bit ATmega 328P (a.k.a Arduino Uno) For purposes of this exercise, let's say that the ATmega328 has 4 regular GPIO ports; A, B, C, and D, each with 8 pins. Every GPIO port has three registers (outlined in table below) PORTX: used to write output on a pin on port X that is configured as an output. When a pin is configured as an input, writing a 1 to its bit in PORTX activates a pull-up resistor for that pin, and writing a 0 to its bit in PORTX de-activates the pull-up resistor for that pin DDRX: is the data direction register for port X. Writing a 0 to a bit in DDRX makes the corresponding port pin an input, while writing a 1 to a bit in DDRX makes the corresponding port pin an output. PINX: is the input register, used to read input data on port X. If a pin is configured as an output, then reading the input register bit corresponding to that pin will give you the value that was last output on the port. Now see the following macro below #define PORTB (*(volatile unsigned char *)0x25) Bit 0 Address 0e08 0:28) 0D9 0129 007 10127) Bit 7 Bit 6 Bit 4 Bit 3 Bit 2 Bit 1 Page PORTD PORTD6 PORTDS PORTD PORTDS PORTD2 PORTD1 PORTDO 92 006 0:25) PCRTE PORTB PORTBS 91 PN FINB PINB2 Using the chart above, write similar macros for PORTD, DDRD, and PIND. What is the purpose of the volatile keyword Write C code to configure PORTD pin 3 as output and write a 1 to it, without affecting the other pins on port D. (Two lines of code total) Write C code to configure PORTD pin 6 as input (with a pullup resistor) without affecting the other pins on port D. (Two lines of code total) Write a C setup() function that sets up PORTD pin 1 as an input with pullup resistor and PORTD pin 2 as an output. Now write a C loop) function that "blinks" an LED connected to pin 2 when pin 1 is high (one second period), otherwise the LED is off a. b. C. d. If nothing is connected to pin 1, describe the behavior of the LED What is the purpose of the pull up resistor? a. b.

Answer 1

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