Objective
This project goes through several different reset conditions:Power On Reset (POR),Brown Out Reset (BOR) andWatch Dog Timer (WDT) timeout, and shows how each one works on a328PB Xplained board. Some external circuitry is shown to produce a variable voltage input but an adjustable power supply will also work.
For more details on theAVR® Reset Sources visitAVR Reset Sources Overview.
Materials
Hardware Tools (Optional)
| Tool | About | Purchase |
|---|---|---|
 ATmega328PB Xplained Mini Evaluation Kit | | |
Software Tools
| Tool | About | Installers | Installation Instructions | ||
|---|---|---|---|---|---|
| Windows | Linux | Mac OSX | |||
 Atmel® Studio Integrated Development Environment | | | | | |
Exercise Files
| File | Download | Installation Instructions | ||
|---|---|---|---|---|
| Windows | Linux | Mac OSX | ||
Project and Source Files | | | | |
Additional Files
| Files |
|---|
Connection Diagram
Procedure
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Task 1 - Project Open and Build
- Download the project source files from the Exercise Files section above and unzip it to your computer.
- Open Atmel Studio 7
- SelectFile > Open > Project/Solution
- SelectATMEGA328PB_HFO_WDT_Final.atsln from the downloaded project files.
- From the Build menu select 'Rebuild Solution'.
Select 'GCC C Executable Project' and give it the nameProject1. Choose a location to save the project on your computer.
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Task 2 - Board Preparation
Make sure the USB Cable is connected between the board and the PC.
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Task 3 - Programmer Settings
If debugWire is enabled, please disable it.
DWEN
Configuring the DWEN fuse to enable the debugWIRE interface on the Reset pin
This is a confusing, but recoverable condition.
Unless you are an experienced AVR user, it might not be obvious that the one-wire debugWIRE interface utilizes the Reset pin. Enabling the debugWIRE interface disables the use of the Reset pin. The ISP interface requires access to the Reset pin so it’s no longer functional when debugWIRE is enabled. By default, debugWIRE is disabled (fuse bit is set to1). It is enabled whenever a debug session is started in Studio.
RECOVERY
If it’s enabled it can’t be disabled through the standardDevice Programming window option in the studio because that option requires a functional ISP interface. There is, however, a trick to disabling the debugWIRE interface without having to use the HVPP or HVSP interface. A project must be created in Studio targeting the specific Tiny or Mega device being used. Then a debug session needs to be started by selectingDebug > Attach to Target, then exited by choosing theDebug > Disable debugWire and Close option, as shown:
TIP: When you're finished with a debug session in Studio, select theDebug > Disable debugWire and Close option in order to enable device ISP programming.
- ClickTools > Device Programming:
- Click the buttons which are marked as red arrows in the screenshot.
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Task 4 - Programming the Fuse Bits
- Select the 'Fuses' options in the left option bar and set the bits as shown in the figure, which will enable CFD, BOD threshold as 2.7 V, and External Clock.
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Task 5 - Device Programming
Select the 'Memories' options in the left option bar and finish the steps as shown in the figure, which programs the compiled binary file into ATMEGA328PB.
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Task 6 - Project Code
Here is the full code that we reference.
You can also download this in the Exercise Section.
/** ATMEGA328PB_HFO_WDT_Final.c** Created: 2017/03/08 17:15:35* Author : A17582*/#define F_CPU 8000000UL#include <avr/io.h>#include <avr/interrupt.h>#include <avr/wdt.h>#include <util/delay.h>//initialize watchdogvoid WDT_Init(void){ //disable interrupts cli(); WDTCSR = (1<<WDCE )|(1<<WDE ); // Enable configuration change. WDTCSR = (1<<WDIE)| // Enable Watchdog Interrupt Mode. (1<<WDCE )|(1<<WDE )| // Enable Watchdog System Reset Mode if unintentionally enabled. (0<<WDP3 )|(1<<WDP2 )|(1<<WDP1)|(1<<WDP0); // Set Watchdog Timeout period to 4.0 sec. //Enable global interrupts sei();}//Watchdog timeout ISRISR(WDT_vect){ //Burst of 0.1Hz pulses for (uint8_t i=0;i<4;i++) { //LED OFF PORTB &= ~(1 << PINB5); // Set PORTB5 Low _delay_ms(80); //LED ON PORTB |= (1 << PINB5); // Set PORTB5 On _delay_ms(20); }}#define BORFbit 2#define PORFbit 0int main(void){ unsigned char i; DDRB |= (1 << PINB5); // Set PORTB5 as output , DDRB &= ~(1<<PINB7); //Set PORTB7 as input if(MCUSR & 1 ){ MCUSR=0; for ( i=0;i<4;i++) { //LED OFF PORTB &= ~(1 << PINB5); // Set PORTB5 Low _delay_ms(300); //LED ON PORTB |= (1 << PINB5); // Set PORTB5 On _delay_ms(300); } } else if(MCUSR & 4) { MCUSR=0; for (i=0;i<8;i++) { //LED OFF PORTB &= ~(1 << PINB5); // Set PORTB5 Low _delay_ms(100); //LED ON PORTB |= (1 << PINB5); // Set PORTB5 On _delay_ms(100); } } else if(MCUSR & 8) { MCUSR=0; WDT_Init(); for (i=0;i<8;i++) { wdt_reset(); //LED OFF PORTB &= ~(1 << PINB5); // Set PORTB5 Low _delay_ms(20); //LED ON PORTB |= (1 << PINB5); // Set PORTB5 On _delay_ms(80); } MCUSR=0; } //initialize watchdog WDT_Init(); //delay to detect reset //_delay_ms(500); while(1){ PORTB |= (1 << PINB5); // Set PORTB5 high _delay_ms(250); _delay_ms(250); _delay_ms(250); _delay_ms(250); PORTB &= ~(1 << PINB5); // Set PORTB5 Low _delay_ms(250); _delay_ms(250); _delay_ms(250); _delay_ms(250); if((PINB&1<<PINB7)==0){ PORTB |= (1 << PINB5); // Set PORTB5 high _delay_ms(500); _delay_ms(500); _delay_ms(500); _delay_ms(500); _delay_ms(500); _delay_ms(500); _delay_ms(500); _delay_ms(500); } wdt_reset(); }}7
Task 7 - Reset Test Circuit
- Build the Reset test circuit shown in the schematic.
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Task 8 - POR Test
- Pull out the USB Cable
- Make sure the External Adjustable VCC Cable’s switch is at right side (3.2 V)
- Clip The External adjustable VCC cable to the board
- Result: The orange LED will respond by flashing (0.3 ms, four times) based on the code section below because the POR reset is detected.
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Task 9 - BOR Test
- After the POR test, slide the switch on the External Adjustable VCC Cable to the left side (2.5 V)
- Slide the switch on the External Adjustable VCC Cable back to the right side (3.2 V)
- Result: the orange LED will respond by flashing (0.1 ms, eight times) based on the code highlighted below because the BOR reset is detected.
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Task 10 - WDT Test
- Push the Button on the board for about 1 second and then release the button. Extended delays will be triggered in the main routine, which will cause a WDT timeout.
Note: The WDT timer is set to 2 seconds.
- Result: the orange LED will respond by fast flashing (0.02 ms on, 0.08 ms off, four times) at first as the WDT interrupt ISR:
- Result: the orange LED will again respond by fast flashing (0.02 ms on, 0.08 ms off, four times) as the WDT reset is detected:
Analysis
The project shows three ways that a reset can occur: POR, BOR and WDT Timeout. Each has a unique application and can all run in the same application. The code examples are just a reference to how these types of resets can be set up and implemented.
Conclusions
The project helps explain how the reset circuitry within the AVR functions and how to implement it. The code section can be reused in future applications that may require a similar reset structure. By no means is this the only way to design resets in the AVR device, this is just a simple sample project that helps explain the operation and allows you to apply your knowledge and understanding of the reset structure to a specific application.
