Microcomputers Notes
This semester Im taking Microcomputers and this is a study guide/cheat sheet I’m writing to help me better understand my notes and to help anyone else understand the topic who maybe in similar boat. The sections are broken up into an Introduction, followed by what each Exam will cover.
Textbook:
School: Florida Polytechnic University
Table of Contents:
i. Introduction
ii. Exam 1 Material
Exam 1 will cover Chapter 1–5
What to know about AVR 328 Board:
What is Assembly?:
Functions to know:
LDI
IN/OUT
STS
JMP
CBI
SBC
SBCI
ADD
SUBI
iii. Exam 1 Summary
Chapter 1 — 5
iv. Exam 2 Material
v. Exam 2 Summary
vi. Exam 3 Material
vii. Exam 3 Summary
Introduction:
What is a microcomputer?
Microcomputer vs microprocessor vs microcontroller?
What is an Arduino?
What is assembly?
What is a register
Exam 1:
Using assembly to control registers
Flags and how they work
- BRNE checks for Z flag
- Use DEC to change Z flags
- 255 is the maximum number of loops
- All registers keep a maximum of 255 bits
- Create a nested loop to run a loop more than 255 times
ex:
This loops 9 times 100 more times
LDI R20, 100
L2: LDI R16,9
L1:ADD R16, 1
DEC R16
BRNE L2
Practice
This loops any number of times times until reaches a value of 27
LDI R20, 0
L1: ADD R20, R16←Number of times to loop the nested loop
LDI R17, 2 ← load 1 into register R16
ADD R16, R17← Loads 4 into register R15
LDI R17, 27 ← Adds 2 to R16
SUB R17, R16
BRCC L1
Stack, Push, Pop
Calling a function
Stack is a piece of ram (usually at the end of registers)
Stacks are architected as Last in first Out [LIFO]
Push Rr
[SP] =Rr ←save register value in stack pointer
SP = SP -1 ←decrement Stack pointer by 1
POP Rd
SP = SP + 1 ←Increment Stack pointer by 1
Rd = [SP] ←save stack pointer value in register
Push R20
Push R30
POP R16
Pointer:
An address saved in a variable
Stack Pointers are 16 bits in size; Two 8 registers →[SP Low & SP High]
How to setup stack pointer
- You have to use a stack pointer with Push and Pop commands and it is essentially a place to store data but it is ordered based on the order it was pushed
General Purpose register: The structure of I/O pins
Setting the DDRP
Exam 1 Summary:
Overview:
Functions covered in assembly:
Exam 2:
Problem 1 (20 Points)
Write an assembly program to copy 100 bytes of data starting at RAM address $1FF to RAM locations starting at $2FC.
Problem 2 (20 Points)
Write an Assembly program that finds the position of the first low in an 8-bit data item and save
the position in R17. The data is scanned from D0 to D7. Consider the data item is $A7.
Problem 3 (20 points)
1. Write only ONE Assembly instruction to clear bit 4, 2, 0 in R16, without disturbing other bits.
(don’t use LDI)
2. Write only ONE Assembly instruction to set bit 4, 2, 0 in R16, without disturbing other bits.
(don’t use LDI)
3. Find the TCCR1A and TCCR1B values for CTC mode, no presacral, with the clock
coming from the AVR’s crystal
4. State the differences between Timer0 and Timer1.
Problem 4 (20 Points)
Write a C program to count up Port D from 0–99 continuously.
Problem 5 (20 Points)
Assume that XTAL = 16 MHZ. Find the values to be loaded in TCNT0 and OCR0A to generate a time delay
of 10 us in two modes:
a- using Normal mode, no prescalar mode.
b- using CTC mode, no prescalar mode.
Exam 3:
EEL 4746 Final Review Questions
Review: I/O registers: DDRx, PORTx, PINx
1. configure Port, specific bit as input/output
2. What is the maximum delay that can generated by our 16-bit Timer 1 with a prescaler value of 1024 and clock frequency of 16 MHz.
3. In which register can you find the global interrupt enable bit?
4. Where can you find the Interrupt Vector Table (IVT)?
5. When an interrupt is triggered, what register is placed on the stack? Why is this register saved?
6. What immediately happens when an interrupt occurs?
7. What is instruction is required to return from an Interrupt?
8. In what way is a ret instruction different from an reti instruction?
9. What is one of the last things and ISR does before it returns control to the interrupted program?
10. How many bits need to be set for a Timer/Counter 1 Overflow interrupt to be triggered?
11. What triggers a Timer/Counter 1 Overflow Interrupt?
12. Using a single bit instructions, disable all interrupts.
13. Write Assembly code to implement the following circuit.
14. Write an instruction to divide a signed number in register R22 by 2?
15. Write an instruction to multiply an unsigned number in register R22 by 2?
Steps in enabling an interrupt:
Enable the general interrupt : set bit 7 (I) of the SREG to High.
Enable the actual interrupt: set the interrupt bit of the corresponding register to High.
Timer interrupts: TIMSK0, TIMSK1, TIMSK2
External Interrupts: PD2, PD3
Pin change interrupt:
UART:
UDR = Data
Example 1:
sending character ‘G’ continuously (8 bits, 9600 baudrate, 16MHz)
#include <avr/io.h>
Int main (void)
{
UCSR0B = (1<<TXEN0)|(1<<UDRIE0);
UCSR0C = (1<<UCSZ01)|(1<<UCSZ00);
UBRR0L = 103; //baud rate = 9600bps
Sei();
While (1);
Return 0;
}
ISR (USART_UDRE_vect)
{
UDR0=’G’;
}
Example 2:
Receiving bytes of data continuously (8 bits, 9600 baudrate, 16MHz)
#include <avr/io.h>
Int main (void) {
UCSR0B = (1<<RXEN0)|(1<<RXCIE0);
UCSR0C = (1<<UCSZ01)|(1<<UCSZ00);
UBRR0L = 103; //baud rate = 9600bps
Sei();
While (1);
Return 0;
}
ISR (USART_RX_vect) {
PORTB=UDR0;
}
Previous Year Final
Question 1
We would like to design a multiplexer using ATmega328P. The multiplexer is functioning as follows:
PortD.0, PortD.1, and PortD.2 are inputs
PortD.3 is an output.
If the input PortD.2 is 0, then the output must be the same as the input PortD.0
If the input PortD.2 is 1, then the output must be the same as the input PortD.1
(a) [10 pts] Describe your method/idea without using assembly instructions.
Set the Data Direction register to input for Bits 0–2 in PORTD and set the Data direction register for PORTD.3 to output.
Whenever PortD.2 is 0 copy the data in PortD.0 to PortD.3.
Also if PortD.2 is 1 copy the data in PortD.1 to PortD.3.
To Check the status of PortD.2 use SBIC or SBIS.
(b) [40 pts] Implement your method/idea as an assembly program using assembly instructions (without changing the status of other pins on PortD).
LDI R16, 0x08
OUT DDRD, R16
SBIS PORTD, 2
RJMP LOW
RJMP HIGH
HIGH:SBIS PIND, O
RJMP LOOP
SBI PORTD, 3
RJMP END
LOOP:CBI PORTD, 3
RJMP END
LOW: SBIS PIND, 1
RJMP LOOP
SBI PORTD, 3
END: RJMP END
Question 2
We have an ATmega328P based system with 16MHz crystal. We would like to design a transmitter device for a communication system which supports only two different messages:
• To send a message meaning SLOWER, we send the character “S” or “s” over a serial connection
• To send a message meaning FASTER, we send the character “F” or “f” over a serial connection
We would like to use the serial port, PortD.1, to transmit these characters.
(a) [10 pts] Write a C subprogram to initialize the serial port and set the baud rate to 9600bps.
#include <avr/io.h>
Void setup(){
UCSROB = (1<<TXEN0);
UCSROC = (1<<UCSZ01)|(1<<UCSZ00);
UBRROL = 103; // BR=F/((UBRR+1)16)
// 9600=(16*10⁶)/((UBRR+1)16)
// UBRR=103.17
}
(b) [20 pts] Write a C program, which reads PortB.1 continuously and functions as follows:
If PortB.1 is 0 then send the message SLOWER, if PortB.1 is 1 then send the message FASTER.
void send(char c){
while(!(UCSR0A & (1<<UDRE0)));
UCSROC = (1<<UCSZ01)|(1<<UCSZ00);
UDR0 = C;
}
int main(){
setup();
while(1){
DDRD = 0xFF;
PORTD = UDR0;
DDRB = 0;
PINB = (1<<1);
if(PINB==0)
send(‘s’);
else
send(‘f’);
}
return 0;
}
Question 3
[20 pts] We would like to design a serial port receiver system (ATmega328P based with 16MHz crystal) which will use the serial port, PortD.0, to receive characters. Your design must be C based, and it should basically do the following:
If the received character is “S” or “s”, set PortB.2 to LOW
If the received character is “F” or “f”, set PortB.2 to HIGH
You can assume that the serial port is already initialized in receive mode with 9600 bps baud rate.
You don’t need the solution of Question 2 to be able to solve this question.
#include <avr/io.h>
void setup(){
UCSROB = (1<<TXEN0);
UCSROC = (1<<UCSZ01)|(1<<UCSZ00);
UBRROL = 103; // BR=F/((UBRR+1)16)
// 9600=(16*10⁶)/((UBRR+1)16)
// UBRR=103.17
}
int main(){
setup();
while(!(UCSR0A & (1<<RXC0))){
DDRD = 0xFF;
PORTD = UDR0;
if(PORTD==‘s’|| PORTD ==‘S’ )
PORTB = (0<<2);
else if (PORTD==‘f’ || PORTD==‘F’)
PORTB = ~(0<<2);
}
return 0;
}
Resources:
Thank you again for reading and enjoying this journey with me!
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