AVR I/O programming Atmega 64 uNiboard ThinkLABS maaniq

Embedded Systems
Be Ready for Tomorrow…
By,
PL.Manicka Raja,
Embedded & Robotics Engineer,
ThinkLABS Techno Solutions Pvt Ltd,
SINE, IIT-Bombay, Mumbai.
manicka.r@thinklabs.in

What is Embedded Systems?
© 2013, www.thinklabs.in 2

About Microcontroller
ATmega64
AT - ???
Mega - ???
64 - ???

KEY Notes
REGISTERS…?
Types of Registers
General Purpose Registers
Special Registers

GENERAL PURPOSE – I/O
DDRx …..
PORTx
PINx
Where X represents
A,B,C,D….F,G.

Special Purpose
UART
TIMERS
ADC
SPI
I2C
EEPROM

8 - BIT REGISTER ACCESSING
7 6 5 4 3 2 1 0
MSB…… …..LSB

Output
 Step 1 : Configuration or Initialization
 DDRx =
 1 – Output,
 0 – input
 Step 2 : Status
 PORTx =
 1 – Logic High ( 5 volts)
 0 – Logic Low (0 volts)
 Where X represents A,B,C,D….F,G.

BLINK LED - Program
#include<avr/io.h>
void main()
{
DDRC=OxFF; // Configuration
PORTC=OxOO; // All LEDS - ON, Active Low
PORTC=OxFF; // All LEDS - OFF,
}

BLINK LED - Program
#include<avr/io.h>
void main()
{
while(1) // super loop
{
}
}

BLINK LED - Program
#include<avr/io.h>
#include<util/delay.h>
void main()
{
{
_delay_ms(1000);
_delay_ms(1000);
}
}

INPUT

INPUT
© 2013, www.thinklabs.in
Vcc
22

INPUT
Vcc
23

INPUT
Vcc
24

Functions of PORTx Register in
GPIO
Output Input
DDRx 1 0
PORTx
1 0 1 0
Logic High Logic Low Enable Internal Pull-
Up
Disable Internal
Pull-Up
5 volts 0 volts Stable state - 1 Floating state ( 0 or 1)

Input
 Step 1 : Configuration or Initialization
 DDRx =
 Step 2 : Pull – Up
 PORTx =
 1 – Enable Pull – UP
 0 – Disable Pull – UP
 Step 3 : Checking
 1 – Switch is not pressed
 0 – Switch is pressed
 Switches are Active Low, When pressed , it gives 0.

MSB……….LSB = Big Endian.
•7654 3210
•1010 1010
• (1<< position )
• (1<<4)
BIT WISE OPERATIONS
35

BIT WISE OPERATIONS
Why we need BITWISE operations…?
To change only our desired bit
without affecting any other Bits in
the REGISTER.
When Individual Accessing is required
When the port is both Input & Output.

BIT WISE OPERATIONS
 SET BIT
 To make the desired position as LOGIC 1 (ONE)
 CLEAR BIT
 To make the desired position as LOGIC 0 (ZERO)
 CHECK BIT
 To know whether the desired position is 0 or 1
(Without affecting any other bits)

SET Bit - Explanation
 a = 01101010;
 Desired Position is 4
 So, OR function
0 1 1 O 1 0 1 0 is a
0 0 0 1 0 0 0 0 is (1<<pos) ….(1<<4)
-----------------------
0 1 1 1 1 0 1 0 is a= a|(1<<pos); x=x+5;
----------------------- a|=(1<<pos); x+=5;
Important Note : Rest of the BITS are not affected

One’s complement
• 0001 0000 is (1<<4)
• One’s Complement…?
• 1110 1111 is one’s complement of (1<<4)
•~ is negation , used to produce one’s
complement of a number.
• 11101111 is ~(1<<4)

CLEAR Bit - Explanation
 a = 0110 1010;
 Desired Position is 5
 So, AND function
0 1 1 0 1 0 1 0 is a
1 1 0 1 1 1 1 1 is ~(1<<pos) or ~(1<<5)
-----------------------
0 1 0 0 1 0 1 0 is a= a&~(1<<pos); x=x+5;
----------------------- a&=~(1<<pos); x+=5;
Important Note : Rest of the BITS are not affected
41

SET BIT
REGISTER |= (1<<pos)
|= OR Equal to

CLEAR BIT
REGISTER &=~ (1<<pos)
&= ~ AND equal to negation

CHECK BIT
(REGISTER & (1<<pos))== ?
& AND is only for checking, not for assingning
 EQUAL ‘=’ is for assigning, BUT here we don’t assign
anything,
 Just checking the Status of the BIT

Multiple SET BIT
REGISTER |= ( refer below)
|=
((1<<7) | (1<<5) | (1<<2))

Multiple CLEAR BIT
REGISTER &=~ ( refer below)
&=~
((1<<7) | (1<<5) | (1<<2))

Switch Program
#include<avr/io.h>
void main()
{
DDRD&=~(1<<6); // PORTD 6th pin is SW1
PORTD|=(1<<6); //PULL – UP resistor
{
if( (PIND & (1<<6)) == O )
{
_delay_ms(1000);
}
}
} © 2013, www.thinklabs.in 47

Switch Program
#include<avr/io.h>
#define SW1 (PIND & (1<<6)) // macro for SW1
void main()
{
DDRD&=~(1<<PD6); // PD6 is already #defined as 6 @ avr/ io.h
PORTD|=(1<<PD6); //PULL – UP resistor
{
if( SW1 == O )
{
_delay_ms(1000);
}

Direct OPERATION for REGISTERS
 7..4 – o/p
 3...0 – i/p
DDRC = 0b11110000;
(or)
DDRC = 0xF0;
 0 – input
 1- output

Bitwise OPERATION for REGISTERS
 7..4 – o/p
 3...0 – i/p
DDRC |=
((1<<7)|(1<<6)|(1<<5)|(1<<4));
(and also)
DDRC &=~
((1<<3)|(1<<2)|(1<<1)|(1<<0));

Key Notes for An Embedded Developer
What is a Compiler?
What is a Cross–Compiler..?
Diff B/W uC & uP
CISC & RISC…?
Architecture…?
= Program memory & Data Memory

Compiler
 The process of converting high level language to the
machine level language
 For the SAME processor.
 Example : Turbo C, Dev C
 Programs are compiled &
 Output is viewed on the SAME System

Cross -Compiler
 The process of converting high level language to the
machine level language
 For the TARGET processor.
 Example : winAVR, KeilC, AVR Studio
 Programs are compiled in a system &
 Output is viewed on ANOTHER System

5 Golden Rules for Programming
also called as Cross Compilation
1. Make New Separate folder for Each &
Every Program
2. Only Makefile and .c (dot C) file…?
3. ‘M ‘of Makefile should be in Capital.
4. Target name in Makefile & some
changes
5. Those three Switches in your uNiBoard

Tools to Remember
To Compile
Tools  Make All
To Program
Tools  Make Program

ReCap
 X= 6;
 Right to Left Operation in C.
 So, We are passing the value 6 to X,
 Similarly,
 DDRx=OxFF, and PORTx=OxFF;
 So, We are (passing) Writing an 8 bit Value to REGISTER
 But, in PINx , we are just only reading from it.
 PINx & (1<< pos )

R/W - Registers
DDRx - Write Only
PORTx - Write Only
PINx - Read Only

AVR I/O programming Atmega 64 uNiboard ThinkLABS maaniq

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