In this tutorial we will learn how to use an External Interrupt in PIC Microcontroller and why/where we will need them. This is a part of the sequence of PIC Tutorials in which we started learning PIC Microcontrollers from scratch; hence this tutorial assumes that you are familiar with how to program a PIC MCU using MPLABX and how to interface an LCD with PIC. If not please fall back to their respective links and read them trough, for I will be skipping most of the information that was already covered there.
Materials Required:
- PIC16F877A Perf Board
- 16x2 LCD Display
- Push Button
- Connecting Wires
- Bread Board
- PicKit 3
What are interrupts and where to use them:
Before getting into how to program PIC microcontroller interrupts, let us understand what an Interrupt actually is and where we would need to use them. Further, there are lots of types of interrupts in Microcontroller and PIC16F877A has about 15 of them. Let us not confuse them all into our head for now.
So! what is an interrupt in Microcontrollers?
As we all know microcontrollers are used to perform a set of pre-defined (programmed) activates which triggers the necessary outputs based on the input. But, while your Microcontroller is busy with executing one piece of code there might be an emergency situation where other piece of your code needs immediate attention. This other piece of code that needs immediate attention should be treated as an interrupt.
For example: Let us consider that you are playing your favourite game on your mobile and the controller (assumption) inside your phone is busy throwing all the graphics that is needed for you to enjoy the game. But, suddenly your girlfriend calls to your number. Now, the worst thing to happen is your mobiles controller to neglecting your girlfriends call since you are busy playing a game. To prevent this nightmare from happening we use something called interrupts.
These interrupts will always be active listing for some particular actions to happen and when they occur they execute a piece of code and then gets back to the normal function. This piece of code is called the interrupt service routine (ISR). One practical project in which interrupt is mandatory is “Digital Speedometer and Odometer Circuit using PIC Microcontroller”
In Microcontrollers there are two main types of interrupts. They are External Interrupt and Internal Interrupt. The internal Interrupts occur inside the Microntroller for performing a task, for example Timer Interrupts, ADC Interrupts etc. These interrupts are triggered by the software to complete the Timer operation or ADC operation respectively.
Menghitung Counter External Interrupt Devices
The external interrupt is the one that can get triggered by the user. In this program we will learn how to use an External interrupt by using a push button to trigger an interrupt. We will use an LCD to display numbers incrementing from 0 to 1000 and when an interrupt is triggered we should notify about it from the Interrupt Service Routine ISR and then continue back to incrementing the numbers.
$begingroup$It's a requirement that I should count the number of button press by external or any other interrupt.
So when I use the external interrupt to increment the counter by 1, it sometimes is crease by 2 or 3 due to debounce. Can anyone tell me how to count accurately in this case?
pb is the pushbutton counter. and num1 and num2 are flags.
So after 4 times pushbutton press I want to do some other task. Simerly after 5 times pushbutton press I want to do another task. so Important is to count an exact number of a button press.I know the debounce principle. But where can I put this debounce delay code as it is interrupt driven?
litun bls
litun blslitun bls
$endgroup$3 Answers
$begingroup$Internal Interrupt
1) It is better, if you can deal with debouncing in hardware itself. If possible, put an appropriate capacitor on the interrupt pin to ground.
2) In software you can deal like: (Assuming that bouncing can last up to 50s)
last_interrupt_time has 0 initial value. The code increments the press value for the very first press. But it will not increment for 50 ms, no matter how many button interrupts come in between due to bouncing. This will efficiently work only if the microcontroller supports interrupts within interrupts, otherwise it has chance of missing timer overflow interrupt.
3) Another method is simply adding a 50 ms delay after incrementing press. It works. But not a good method though.
4) Another idea, by using a flag variable:
flag is a volatile variable shared between main() and ISR. Code is written in main() such that it reinitialises flag back to 0 only after counting 50 ms. So this is like disabling button interrupts for 50 ms. Anyway, Humans cant press faster than that.
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$endgroup$$begingroup$You need to do what is called debouncing. There are many ways, and there is surely much written about it out there.
The method I ususally use is to not consider a new state valid until the input has been in that state for 50 consecutive 1 ms clock interrupts. 50 ms is longer than most switches bounce, but is still instantaneous in human time. Put another way, a human won't notice a 50 ms delay between pressing a button and some action occurring.
In rare cases where the system has to react faster than the debouncing time of the mechanical switch, you can trigger off the first change in state, then block out new changes in state until the existing change has settled. This gives you almost no latency, but does make the system susceptible to short glitches. You have to decide what is actually important.
Again, keep in mind that delays of up to about 50 ms are unnoticed by human users.
Olin LathropOlin Lathrop286k3030 gold badges353353 silver badges806806 bronze badges
$endgroup$$begingroup$It's hard to propose solution without knowing what kind of MCU is that. Do you have any timer or sys tick?
Maybe something like this:
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$begingroup$I'm not quite sure how external interrupts will work with several peripherals on the same EXTI line.
For instance, if I configured interrupt on line X and on the same line(of course another GPIO port) I have SPI MOSI or SCK, or maybe ADC working, would I receive interrupt every time one of these pins was triggered? And if I do then is it possible to get information about what pin was actually triggered?
Thanks.
Long Smith
Long SmithLong Smith
$endgroup$2 Answers
$begingroup$When using a GPIO pin for external interrupt (without setting the alternative function for the pin) you can have exactly one interrupt per line. Hence, you can never have an external interrupt for both PA6 and PB6 since they are located on the same line.
How to get better at battlefront 2. Star Wars Battlefront runs on an updated version of DICE’s, which powers some of the most impressive graphics around. You may have already seen it in action powering Battlefield 4, Battlefield Hardline, or Dragon Age: Inquisition.
However, when you are activating the alternative function for a pin as you would do for SPI and other peripherals you will get the interrupt from the peripheral itself (i.e. another interrupt vector).
You can not configure a pin as both alternative function and as a GPIO pin (with external interrupt).
staringlizardstaringlizard
$endgroup$$begingroup$I/O ports on the STM32F10x are organized into 7 groups of 16, designated PA0, PA1, ..PA15, PB0, .. up to PG15. Typically, only a subset of these are brought out to pins.
To trigger an interrupt, a port must be configured in Input mode.
PAx, PBx, ..PGx (x=0.15) are muxed into External Interrupt Line x, so only one of these ports drives Line x. That port is selected by the EXTIx bit field in the AFIO_EXTICRy (y=1.4) register. The other ports on Line x are ignored as far as external interrupts are concerned.
Line x is unmasked by writing a '1' to the appropriate bit in the EXTI_IMR register, and rising and/or falling edge trigger is selected in the EXTI_RTSR and EXTI_FTSR registers.
For example, to have an external interrupt on PC4 rising, set the EXTI4 bits in the AFIO_EXTICR2 register to (binary) 0010 to select port PC4. Write a '1' to the MR4 bit in EXTI_IMR to enable Line 4, and to TR4 in EXTI_RTSR to select rising edge. (In this case, PA4, PB4, and PD4-PG4 are not available as external interrupt sources.)
The EXTI_PR register can be read to determine which lines have pending interrupts.
The NVIC must be configured to accept and process the interrupt request. External interrupts 0 through 4 have individual interrupt vectors, but 5 through 9 share one vector, as do 10 through 15.
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This tutorial shows the use of timers and interrupts for Arduino boards. As Arduino programmer you have probably used timers and interrupts without even knowing it’s there, because all the low level hardware stuff is hidden by the Arduino API. Many Arduino functions uses timers, for example the time functions: delay(), millis() and micros(), the PWM functions analogWrite(), the tone() and the noTone() function, even the Servo library uses timers and interrupts.
Buy the Arduino from: Banggood | Amazon
A timer, A.K.A. counter is a piece of hardware built in the Arduino controller. It is like a clock, and can be used to measure time events.
The timer can be programmed by some special registers. You can configure the pre-scaler for the timer, or the mode of operation and many other things.
The Arduino board is based on the Atmel AVR ATmega168 or the ATmega328 microchip. These chips are pin compatible and only differ in the size of internal memory. Both have 3 timers, called Timer0, Timer1 and Timer2. Timer0 and Timer2 are 8bit timer, where Timer1 is a 16bit timer.
The most important difference between 8bit and 16bit timer is the timer resolution. 8bits means 256 values (two to the power of 8) where 16bit means 65536 values (two to the power of 16) which is much higher resolution.
The Arduino Mega series is based on the Atmel AVR ATmega1280 or the ATmega2560. They are almost identical to previous chips but only differs in memory size. These chips have 6 timers. First 3 timers (Timer 0, Timer1 and Timer2) are identical to the ATmega168/328. Timer3, Timer4 and Timer5 are all 16bit timers, similar to Timer1.
All timers depends on the system clock of your Arduino system. Normally the system clock is 16MHz, but the Arduino Pro 3/3V is 8Mhz, so be careful when writing your own timer functions.
The timer hardware can be configured with some special timer registers. In the Arduino firmware, all timers were configured to a 1kHz frequency and interrupts are generally enabled.
The timer hardware can be configured with some special timer registers. In the Arduino firmware, all timers were configured to a 1kHz frequency and interrupts are generally enabled.
To summarize:
Different clock sources can be selected for each timer independently. To calculate the timer frequency (for example 2Hz using Timer1) you will need:
1. CPU frequency 16Mhz for Arduino
2. maximum timer counter value (256 for 8bit, 65536 for 16bit timer)
3. Divide CPU frequency through the chosen pre-scaler (16000000 / 256 = 62500)
4. Divide result through the desired frequency (62500 / 2Hz = 31250)
5. Verify the result against the maximum timer counter value (31250 < 65536 success) if fail, choose bigger pre-scaler.
2. maximum timer counter value (256 for 8bit, 65536 for 16bit timer)
3. Divide CPU frequency through the chosen pre-scaler (16000000 / 256 = 62500)
4. Divide result through the desired frequency (62500 / 2Hz = 31250)
5. Verify the result against the maximum timer counter value (31250 < 65536 success) if fail, choose bigger pre-scaler.
Timers can be configured in different modes.
PWM (Pulse width modulation) mode – the OCxy outputs are used to generate PWM signals
CTC (Clear timer on compare match) mode – When the timer counter reaches the compare match register, the timer will be cleared.
CTC (Clear timer on compare match) mode – When the timer counter reaches the compare match register, the timer will be cleared.
The program running on a controller is normally running sequentially instruction by instruction. An interrupt is an external event that interrupts the running program and runs a special interrupt service routine (ISR). After the ISR has been finished, the running program is continued with the next instruction. Instruction means a single machine instruction, not a line of C or C++ code.
Before an pending interrupt will be able to call a ISR the following conditions must be true:
- Interrupts must be generally enabled
- the according Interrupt mask must be enabled
Interrupts can generally enabled or disabled with the function interrupts() or noInterrupts(). By default in the Arduino firmware interrupts are enabled. Interrupt masks are enabled / disabled by setting or clearing bits in the Interrupt mask register (TIMSKx).
How to make laptop into jarvis. When an interrupt occurs, a flag in the interrupt flag register (TIFRx) is been set. This interrupt will be automatically cleared when entering the ISR or by manually clearing the bit in the interrupt flag register.
The Arduino functions attachInterrupt() and detachInterrupt() can only be used for external interrupt pins. These are different interrupt sources, not discussed here.
A timer can generate different types of interrupts. The register and bit definitions can be found in the processor data sheet (Atmega328 or Atmega2560) and in the I/O definition header file (iomx8.h for Arduino, iomxx0_1.h for Arduino Mega in the hardware/tools/avr/include/avr folder). The suffix x stands for the timer number (0.5), the suffix y stands for the output number (A,B,C), for example TIMSK1 (Timer1 interrupt mask register) or OCR2A (Timer2 output compare register A).
Timer Overflow:
Timer overflow means the timer has reached is limit value. When a timer overflow interrupt occurs, the timer overflow bit TOVx will be set in the interrupt flag register TIFRx. When the timer overflow interrupt enable bit TOIEx in the interrupt mask register TIMSKx is set, the timer overflow interrupt service routine ISR(TIMERx_OVF_vect) will be called.
Output Compare Match:
When a output compare match interrupt occurs, the OCFxy flag will be set in the interrupt flag register TIFRx . When the output compare interrupt enable bit OCIExy in the interrupt mask register TIMSKx is set, the output compare match interrupt service ISR(TIMERx_COMPy_vect) routine will be called.
Timer Input Capture:
When a timer input capture interrupt occurs, the input capture flag bit ICFx will be set in the interrupt flag register TIFRx. When the input capture interrupt enable bit ICIEx in the interrupt mask register TIMSKx is set, the timer input capture interrupt service routine ISR(TIMERx_CAPT_vect) will be called.
There is fixed relation between the timers and the PWM capable outputs. When you look in the data sheet or the pinout of the processor these PWM capable pins have names like OCRxA, OCRxB or OCRxC (where x means the timer number 0.5). The PWM functionality is often shared with other pin functionality.
The Arduino has 3 timers and 6 PWM output pins. The punisher game steam. The relation between timers and PWM outputs is:
- Pins 5 and 6: controlled by Timer0
- Pins 9 and 10: controlled by Timer1
- Pins 11 and 3: controlled by Timer2
On the Arduino Mega we have 6 timers and 15 PWM outputs:
- Pins 4 and 13: controlled by Timer0
- Pins 11 and 12: controlled by Timer1
- Pins 9 and10: controlled by Timer2
- Pin 2, 3 and 5: controlled by timer 3
- Pin 6, 7 and 8: controlled by timer 4
- Pin 46, 45 and 44:: controlled by timer 5
Usefull 3rd party libraries
Some 3rd party libraries exists, that uses timers:
- Ken Shirrifs IR library using Timer2 – Send and receive any kind of IR remote signals
- Timer1 and Timer3 library using Timer1 or tiner3 – easy way to write your own timer interrupt service routines.
Blinking LED with compare match interrupt
The first example uses the Timer1 in CTC mode and the compare match interrupt to toggle a LED. The timer is configured for a frequency of 2Hz. The LED is toggled in the interrupt service routine.
[sourcecode language=”cpp”]
/*
* timer and interrupts
* Timer1 compare match interrupt example
* more infos: https://oscarliang.com
*/
* timer and interrupts
* Timer1 compare match interrupt example
* more infos: https://oscarliang.com
*/
#define ledPin 13
void setup()
{
pinMode(ledPin, OUTPUT);
{
pinMode(ledPin, OUTPUT);
// initialize Timer1
noInterrupts(); // disable all interrupts
TCCR1A = 0;
TCCR1B = 0;
TCNT1 = 0;
noInterrupts(); // disable all interrupts
TCCR1A = 0;
TCCR1B = 0;
TCNT1 = 0;
OCR1A = 31250; // compare match register 16MHz/256/2Hz
TCCR1B |= (1 << WGM12); // CTC mode
TCCR1B |= (1 << CS12); // 256 prescaler
TIMSK1 |= (1 << OCIE1A); // enable timer compare interrupt
interrupts(); // enable all interrupts
}
TCCR1B |= (1 << WGM12); // CTC mode
TCCR1B |= (1 << CS12); // 256 prescaler
TIMSK1 |= (1 << OCIE1A); // enable timer compare interrupt
interrupts(); // enable all interrupts
}
ISR(Timer1_COMPA_vect) // timer compare interrupt service routine
{
digitalWrite(ledPin, digitalRead(ledPin) ^ 1); // toggle LED pin
}
{
digitalWrite(ledPin, digitalRead(ledPin) ^ 1); // toggle LED pin
}
void loop()
{
// your program here…
}
{
// your program here…
}
[/sourcecode]
Blinking LED with timer overflow interrupt
same example like before but now we use the timer overflow interrupt. In this case Timer1 is running in normal mode.
The timer must be pre loaded every time in the interrupt service routine.
[sourcecode language=”cpp”]
/*
* timer and interrupts
* Timer1 overflow interrupt example
* more infos: https://oscarliang.com
*/
/*
* timer and interrupts
* Timer1 overflow interrupt example
* more infos: https://oscarliang.com
*/
#define ledPin 13
void setup()
{
pinMode(ledPin, OUTPUT);
{
pinMode(ledPin, OUTPUT);
// initialize Timer1
noInterrupts(); // disable all interrupts
TCCR1A = 0;
TCCR1B = 0;
noInterrupts(); // disable all interrupts
TCCR1A = 0;
TCCR1B = 0;
TCNT1 = 34286; // preload timer 65536-16MHz/256/2Hz
TCCR1B |= (1 << CS12); // 256 prescaler
TIMSK1 |= (1 << TOIE1); // enable timer overflow interrupt
interrupts(); // enable all interrupts
}
TCCR1B |= (1 << CS12); // 256 prescaler
TIMSK1 |= (1 << TOIE1); // enable timer overflow interrupt
interrupts(); // enable all interrupts
}
ISR(Timer1_OVF_vect) // interrupt service routine that wraps a user defined function supplied by attachInterrupt
{
TCNT1 = 34286; // preload timer
digitalWrite(ledPin, digitalRead(ledPin) ^ 1);
}
{
TCNT1 = 34286; // preload timer
digitalWrite(ledPin, digitalRead(ledPin) ^ 1);
}
void loop()
{
// your program here…
}
{
// your program here…
}
[/sourcecode]
Reading quadrature encoders with a timer
The next example uses Timer2 and the compare match interrupt to read the encoder inputs.
Timer2 is initialized by default to a frequency of 1kHz (1ms period). In the interrupt service routine the state of all encoder pins is read and a state machine is used to eliminate false readings. Using the timer interrupt is much easier to handle than using 4 input change interrupts.
The signals of a quadrature encoder is a 2bit Gray code. Only 1 bit is changing from state to state. A state machine is perfect to check the signal and count the encoder ticks. The timer must be fast enough, to recognize each state change. For the Pololu wheel encoders used here, the 1ms timer is fast enough.
The following example has been modified to work with Arduino V1.x
[sourcecode language=”cpp”]
/*
* timer and interrupts
* Timer2 compare interrupt example. Quadrature Encoder
* more infos: https://oscarliang.com
*
* Credits:
* based on code from Peter Dannegger
* http://www.mikrocontroller.net/articles/Drehgeber
*/
#if ARDUINO >= 100
#include “Arduino.h”
#else
#include “WConstants.h”
#endif
* timer and interrupts
* Timer2 compare interrupt example. Quadrature Encoder
* more infos: https://oscarliang.com
*
* Credits:
* based on code from Peter Dannegger
* http://www.mikrocontroller.net/articles/Drehgeber
*/
#if ARDUINO >= 100
#include “Arduino.h”
#else
#include “WConstants.h”
#endif
// Encoder Pins
#define encLtA 2
#define encLtB 3
#define encRtA 11
#define encRtB 12
#define ledPin 13
#define encLtA 2
#define encLtB 3
#define encRtA 11
#define encRtB 12
#define ledPin 13
#define LT_PHASE_A digitalRead(encLtA)
#define LT_PHASE_B digitalRead(encLtB)
#define RT_PHASE_A digitalRead(encRtA)
#define RT_PHASE_B digitalRead(encRtB)
#define LT_PHASE_B digitalRead(encLtB)
#define RT_PHASE_A digitalRead(encRtA)
#define RT_PHASE_B digitalRead(encRtB)
static volatile int8_t encDeltaLt, encDeltaRt;
static int8_t lastLt, lastRt;
int encLt, encRt;
static int8_t lastLt, lastRt;
int encLt, encRt;
ISR( Timer2_COMPA_vect )
{
int8_t val, diff;
{
int8_t val, diff;
digitalWrite(ledPin, HIGH); // toggle LED pin
val = 0;
if( LT_PHASE_A )
val = 3;
if( LT_PHASE_B )
val ^= 1; // convert gray to binary
diff = lastLt – val; // difference last – new
if( diff & 1 ){ // bit 0 = value (1)
lastLt = val; // store new as next last
encDeltaLt += (diff & 2) – 1; // bit 1 = direction (+/-)
}
val = 0;
if( LT_PHASE_A )
val = 3;
if( LT_PHASE_B )
val ^= 1; // convert gray to binary
diff = lastLt – val; // difference last – new
if( diff & 1 ){ // bit 0 = value (1)
lastLt = val; // store new as next last
encDeltaLt += (diff & 2) – 1; // bit 1 = direction (+/-)
}
val = 0;
if( RT_PHASE_A )
val = 3;
if( RT_PHASE_B )
val ^= 1; // convert gray to binary
diff = lastRt – val; // difference last – new
if( diff & 1 ){ // bit 0 = value (1)
lastRt = val; // store new as next last
encDeltaRt += (diff & 2) – 1; // bit 1 = direction (+/-)
}
digitalWrite(ledPin, LOW); // toggle LED pin
}
void QuadratureEncoderInit(void)
{
int8_t val;
if( RT_PHASE_A )
val = 3;
if( RT_PHASE_B )
val ^= 1; // convert gray to binary
diff = lastRt – val; // difference last – new
if( diff & 1 ){ // bit 0 = value (1)
lastRt = val; // store new as next last
encDeltaRt += (diff & 2) – 1; // bit 1 = direction (+/-)
}
digitalWrite(ledPin, LOW); // toggle LED pin
}
void QuadratureEncoderInit(void)
{
int8_t val;
cli();
TIMSK2 |= (1<<OCIE2A);
sei();
pinMode(encLtA, INPUT);
pinMode(encRtA, INPUT);
pinMode(encLtB, INPUT);
pinMode(encRtB, INPUT);
TIMSK2 |= (1<<OCIE2A);
sei();
pinMode(encLtA, INPUT);
pinMode(encRtA, INPUT);
pinMode(encLtB, INPUT);
pinMode(encRtB, INPUT);
val=0;
if (LT_PHASE_A)
val = 3;
if (LT_PHASE_B)
val ^= 1;
lastLt = val;
encDeltaLt = 0;
if (LT_PHASE_A)
val = 3;
if (LT_PHASE_B)
val ^= 1;
lastLt = val;
encDeltaLt = 0;
val=0;
if (RT_PHASE_A)
val = 3;
if (RT_PHASE_B)
val ^= 1;
lastRt = val;
encDeltaRt = 0;
if (RT_PHASE_A)
val = 3;
if (RT_PHASE_B)
val ^= 1;
lastRt = val;
encDeltaRt = 0;
encLt = 0;
encRt = 0;
}
encRt = 0;
}
int8_t QuadratureEncoderReadLt( void ) // read single step encoders
{
int8_t val;
{
int8_t val;
cli();
val = encDeltaLt;
encDeltaLt = 0;
sei();
return val; // counts since last call
}
val = encDeltaLt;
encDeltaLt = 0;
sei();
return val; // counts since last call
}
int8_t QuadratureEncoderReadRt( void ) // read single step encoders
{
int8_t val;
{
int8_t val;
cli();
val = encDeltaRt;
encDeltaRt = 0;
sei();
return val; // counts since last call
}
val = encDeltaRt;
encDeltaRt = 0;
sei();
return val; // counts since last call
}
void setup()
{
Serial.begin(38400);
pinMode(ledPin, OUTPUT);
QuadratureEncoderInit();
}
void loop()
{
encLt += QuadratureEncoderReadLt();
encRt += QuadratureEncoderReadRt();
Serial.print(“Lt: “);
Serial.print(encLt, DEC);
Serial.print(” Rt: “);
Serial.println(encRt, DEC);
delay(1000);
}
[/sourcecode]
{
Serial.begin(38400);
pinMode(ledPin, OUTPUT);
QuadratureEncoderInit();
}
void loop()
{
encLt += QuadratureEncoderReadLt();
encRt += QuadratureEncoderReadRt();
Serial.print(“Lt: “);
Serial.print(encLt, DEC);
Serial.print(” Rt: “);
Serial.println(encRt, DEC);
delay(1000);
}
[/sourcecode]