Difference between revisions of "AVR I/O Register Configuration"

 
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[[Category:AVR Tutorials]]
 
[[Category:AVR Tutorials]]
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[[User:Xplore007|Bagwan]] ([[User talk:Bagwan|talk]])
 
  
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In this tutorial we are going to discuss the port configuration of AVR/Atmel controllers or in general Atmega family. In this tutorial we will be using Atmega32 as reference, same will be applicable to other Atmega series controllers.
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=Objective=
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In this tutorial we are going to discuss the port configuration of AVR/Atmel controllers or in general Atmega family. In this tutorial we will be using Atmega32 as reference, same will be applicable to other Atmega series controllers.<br>
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At the end of this tutorial you will be familiar with the Atmega GPIO's and the associated registers for configuring and accessing the GPIO's.<br>
 
At the end of this tutorial you will be familiar with the Atmega GPIO's and the associated registers for configuring and accessing the GPIO's.<br>
  
 
=GPIO Registers=
 
=GPIO Registers=
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The basic and important feature of the any controllers is the number of gpio's available connecting the peripherals. Atmega32 has 32-gpio's grouped into four 8-bit ports namely PORTA-PORTD as shown in the below image.  
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The basic and important feature of any controllers is the number of gpio's available for connecting the peripherals. Atmega32 has 32-gpio's grouped into four 8-bit ports namely PORTA-PORTD as shown in the below image.  
  
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As shown in the above image many I/O pins have 2-3 functions. If a pin is used for other function then it may not be used as a gpio.
  
 
Though the gpio pins are grouped into 8-bit ports they can still be configured and accessed individually.  
 
Though the gpio pins are grouped into 8-bit ports they can still be configured and accessed individually.  
 
<br>Each Port is associated with 3 registers for direction configuration(Input/Output), read and write operation.
 
<br>Each Port is associated with 3 registers for direction configuration(Input/Output), read and write operation.
  
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{| class="wikitable" style="text-align:center; background-color:#ABCDEF;margin: 1em auto 1em auto"
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{| class="table table-striped table-hover table-condensed table-bordered"
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!Register||  Description
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|-class="info"
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|Register||  Description
 
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|DDRx|| Used to configure the respective PORT as output/input  
 
|DDRx|| Used to configure the respective PORT as output/input  
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|PINx|| Used to Read the data from the port pins
 
|PINx|| Used to Read the data from the port pins
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|}note: Here 'x' could be A,B,C,D so on depending on the number of ports supported by the controller.
  
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The Below registers will be used for Configuring and using the GPIOs registers for sending and receiving the Digital signals.
 
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A structure LPC_GPIOn(n= 0,1,2,3) contains all the registers for required for GPIO operation. Refer lpc17xx.h file for more info on the registers.
 
  
  
  
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<b>PINSEL:</b> GPIO Pins Select Register<br>
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<b>DDRx:</b> Data Direction Register<br>
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Almost all the LPC1768 pins are multiplexed to support more than 1 function. Every GPIO pin has a minimum of one function and max of four functions. The required function can be selected by configuring the PINSEL register. As there can be up to 4 functions associated with a GPIO pin, two bits for each pin are available to select the function. This implies that we need two PINSEL registers to configure a PORT pins.
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Before reading or writing the data from the ports, their direction needs to be set. Unless the PORT is configured as output, the data from the registers will not go to controller pins.
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By this the first 16(P0.0-P0.16) pin functions of PORT0 can be selected by 32 bits of PINSELO register. The remaining 16 bits(P0.16-P0.32) are configured using 32bits of PINSEL1 register. 
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As mentioned earlier every pin has max of four functions. Below table shows how to select the function for a particular pin using two bits of the PINSEL register.
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{| class="wikitable" style="text-align:center; background-color:#ABCDEF;margin: 1em auto 1em auto"
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!Value||  Function || Enumeration
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|00|| Primary (default) function, typically GPIO port || PINSEL_FUNC_0
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|01|| First alternate function || PINSEL_FUNC_1
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|10|| Second alternate function || PINSEL_FUNC_2
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|11|| Third alternate function || PINSEL_FUNC_3
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|}
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This register is used to configure the PORT pins as Input or Output. Writing 1's to DDRx will make the corresponding PORTx pins as output. Similarly writing 0's to DDRx will make the corresponding PORTx pins as Input.
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<syntaxhighlight>
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DDRB = 0xff;  // Configure PORTB as Output.
  
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DDRC = 0x00; // Configure PORTC as Input.
  
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<b>FIODIR:</b>Fast GPIO Direction Control Register.<br>This register individually controls the direction of each port pin.
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DDRD = 0x0F; // Configure lower nibble of PORTD as Output and higher nibble as Input
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{| class="wikitable" style="text-align:center; background-color:#ABCDEF;margin: 1em auto 1em auto"
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!Values|| Direction
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|0|| Input
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|1|| Output
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|}
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DDRD = (1<<PD0) | (1<PD3) | (1<<PD6); // Configure PD0,PD3,PD6 as Output and others as Input
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</syntaxhighlight> 
  
  
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<b>FIOSET:</b>Fast Port Output Set Register.<br>This register controls the state of output pins. Writing 1s produces highs at the corresponding port pins. Writing 0s has no effect. Reading this register returns the current contents of the port output register not the physical port value.
 
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{| class="wikitable" style="text-align:center; background-color:#ABCDEF;margin: 1em auto 1em auto"
 
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!Values||  FIOSET
 
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|0|| No Effect
 
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|1|| Sets High on Pin
 
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|}
 
  
  
  
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<b>FIOCLR:</b>Fast Port Output Clear Register.<br>This register controls the state of output pins. Writing 1s produces lows at the corresponding port pins. Writing 0s has no effect.  
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<b>PORTx:</b><br>
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{| class="wikitable" style="text-align:center; background-color:#ABCDEF;margin: 1em auto 1em auto"
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This register is used to send the data to port pins. Writing 1's to PORTx will make the corresponding PORTx pins as HIGH. Similarly writing 0's to PORTx will make the corresponding PORTx pins as LOW.
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!Values||    FIOCLR
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<syntaxhighlight>
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PORTB = 0xff;  // Make all PORTB pins HIGH.
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|0|| No Effect
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PORTC = 0x00; // Make all PORTC pins LOW..
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|1|| Sets Low on Pin
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PORTD = 0x0F; // Make lower nibble of PORTD as HIGH and higher nibble as LOW
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PORTD = (1<<PD0) | (1<PD3) | (1<<PD6); // Make PD0,PD3,PD6 HIGH,
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</syntaxhighlight> 
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<b>PINx:</b>PORT Input Register<br>
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This register is used to read the data from the port pins. Before reading the data from the port pins,  the ports needs to be configured as Inputs.
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<syntaxhighlight>
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DDRB  = 0x00; // Configure the PORTB as Input.
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value = PINB;  // Read the data from PORTB.
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DDRB = 0x00; // Configure PORTB as Input
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DDRD = 0xff;  // Configure PORTD as Output
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PORTD = PINB; // Read the data from PORTB and send it to PORTD.
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</syntaxhighlight>
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<b>Enabling Internal Pull Up Resistors:</b><br>
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Making the DDRx bits to 0 will configure the PORTx as Input. Now the corresponding bits in PORTx register can be used to enable/disable pull-up resistors associated with that pin.To enable pull-up resistor, set bit in PORTx to 1, and to disable set it to 0.
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<syntaxhighlight>
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DDRB  = 0x00; // Configure the PORTB as Input.
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PORTB = 0xFF;  // Enable the internal Pull Up resistor of PORTB.
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DDRD = 0xff;  // Configure PORTD as Output
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PORTD = PINB; // Read the data from PORTB and send it to PORTD.
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</syntaxhighlight>
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=Led Blinking Example=
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After knowing how to configure the GPIO ports, its time to write a simple program to blink the Leds.
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<br>Below points needs to be considered for this example.
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* Include the io.h file as it has the definitions for all the PORT registers.
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* Include delay.h file to use the delay functions.
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* Configure the PORT as Output before writing any data to PORT pins.
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<html>
 +
<script src="https://gist.github.com/SaheblalBagwan/a671ac5b9c722f350a9d.js"></script>
 +
</html>
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==Led Blinking Wiring Diagram==
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[[File:Blink bb.png|x480px|center]]
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=Led and Switches=
 +
<html>
 +
<script src="https://gist.github.com/SaheblalBagwan/310b1582e0bec2ad28ad.js"></script>
 +
</html>
 +
 
 +
==LEDs and Switches Wiring diagram==
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<html><img src ="https://www.exploreembedded.com/blog/wp-content/uploads/img-collections/fritzing-tutorials_de69ccc2/switch_bb.png" width="670 px"></html>
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<b>FIOPIN:</b>Fast Port Pin Value Register.<br>This register is used for both reading and writing data from/to the PORT.<br>
 
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<b>Output:</b> Writing to this register places corresponding values in all bits of the particular PORT pins.<br>
 
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<b>Input:</b>  The current state of digital port pins can be read from this register, regardless of pin direction or alternate function selection (as long as pins are not configured as an input to ADC).<br>
 
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<b>Note:</b>It is recommended to configure the PORT direction and pin function before using it.
 
  
  
  
 +
=Explore Ultra AVR Dev Kit=
 +
The Explore Ultra AVR Kit comes with all the things required, not just for this experiment but for the entire series. And even if you think of migrating to PIC or Arduino, you'll have breakout boards that fit on to this, hence we believe it is a great investment for learning hands on Embedded Systems. The kit is fully open source, you may use the schematics, the design files and all of the source code and build something cool on your own. And when you do that do not forget to share with us what you've done. We would be happy to see you building something cool.
 +
<html>
 +
<ul>
 +
<li>Explore Ultra AVR Dev Kit: <a https://www.exploreembedded.com/product/Explore%20Ultra%20AVR%20Dev%20Kit> Buy from EE Store </a></li>
 +
<a href="https://www.exploreembedded.com/product/Explore%20Ultra%20AVR%20Dev%20Kit">
 +
<img src ="https://www.exploreembedded.com/blog/wp-content/uploads/img-collections/explore-avr-pic-kit/1-dsc03897.jpg" width="480 px">
 +
</a>
 +
</ul>
 +
</html>
  
  
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As all the Atmega Ports and SFR's(Special Function Registers) are defined in io.h, this has to be included at the beginning of the project/code.
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Have a opinion, suggestion , question or feedback about the article let it out here!
 +
{{DISQUS}}

Latest revision as of 14:25, 3 May 2016


In this tutorial we are going to discuss the port configuration of AVR/Atmel controllers or in general Atmega family. In this tutorial we will be using Atmega32 as reference, same will be applicable to other Atmega series controllers.

At the end of this tutorial you will be familiar with the Atmega GPIO's and the associated registers for configuring and accessing the GPIO's.

GPIO Registers

The basic and important feature of any controllers is the number of gpio's available for connecting the peripherals. Atmega32 has 32-gpio's grouped into four 8-bit ports namely PORTA-PORTD as shown in the below image.


As shown in the above image many I/O pins have 2-3 functions. If a pin is used for other function then it may not be used as a gpio.

Though the gpio pins are grouped into 8-bit ports they can still be configured and accessed individually.
Each Port is associated with 3 registers for direction configuration(Input/Output), read and write operation.

Register Description
DDRx Used to configure the respective PORT as output/input
PORTx Used to write the data to the Port pins
PINx Used to Read the data from the port pins
note: Here 'x' could be A,B,C,D so on depending on the number of ports supported by the controller.



DDRx: Data Direction Register
Before reading or writing the data from the ports, their direction needs to be set. Unless the PORT is configured as output, the data from the registers will not go to controller pins.

This register is used to configure the PORT pins as Input or Output. Writing 1's to DDRx will make the corresponding PORTx pins as output. Similarly writing 0's to DDRx will make the corresponding PORTx pins as Input. 

DDRB = 0xff;  // Configure PORTB as Output.
 
DDRC = 0x00; // Configure PORTC as Input.
 
DDRD = 0x0F; // Configure lower nibble of PORTD as Output and higher nibble as Input
 
DDRD = (1<<PD0) | (1<PD3) | (1<<PD6); // Configure PD0,PD3,PD6 as Output and others as Input



PORTx:
This register is used to send the data to port pins. Writing 1's to PORTx will make the corresponding PORTx pins as HIGH. Similarly writing 0's to PORTx will make the corresponding PORTx pins as LOW. 

PORTB = 0xff;  // Make all PORTB pins HIGH.
 
PORTC = 0x00; // Make all PORTC pins LOW..
 
PORTD = 0x0F; // Make lower nibble of PORTD as HIGH and higher nibble as LOW 
 
PORTD = (1<<PD0) | (1<PD3) | (1<<PD6); // Make PD0,PD3,PD6 HIGH,




PINx:PORT Input Register
This register is used to read the data from the port pins. Before reading the data from the port pins, the ports needs to be configured as Inputs. 

DDRB  = 0x00; // Configure the PORTB as Input. 
value = PINB;  // Read the data from PORTB.
 
 
DDRB = 0x00; // Configure PORTB as Input
DDRD = 0xff;  // Configure PORTD as Output
PORTD = PINB; // Read the data from PORTB and send it to PORTD.




Enabling Internal Pull Up Resistors:
Making the DDRx bits to 0 will configure the PORTx as Input. Now the corresponding bits in PORTx register can be used to enable/disable pull-up resistors associated with that pin.To enable pull-up resistor, set bit in PORTx to 1, and to disable set it to 0. 

DDRB  = 0x00;  // Configure the PORTB as Input. 
PORTB = 0xFF;  // Enable the internal Pull Up resistor of PORTB.
 
DDRD = 0xff;  // Configure PORTD as Output
PORTD = PINB; // Read the data from PORTB and send it to PORTD.

Led Blinking Example

After knowing how to configure the GPIO ports, its time to write a simple program to blink the Leds.
Below points needs to be considered for this example.

  • Include the io.h file as it has the definitions for all the PORT registers.
  • Include delay.h file to use the delay functions.
  • Configure the PORT as Output before writing any data to PORT pins.

Led Blinking Wiring Diagram

Blink bb.png



Led and Switches

LEDs and Switches Wiring diagram





Explore Ultra AVR Dev Kit

The Explore Ultra AVR Kit comes with all the things required, not just for this experiment but for the entire series. And even if you think of migrating to PIC or Arduino, you'll have breakout boards that fit on to this, hence we believe it is a great investment for learning hands on Embedded Systems. The kit is fully open source, you may use the schematics, the design files and all of the source code and build something cool on your own. And when you do that do not forget to share with us what you've done. We would be happy to see you building something cool.


Have a opinion, suggestion , question or feedback about the article let it out here!

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