PA UNIT 3 (FR INFORMATION TECHNOLOGY) SPPU
- 2. Interrupt Vs Polling •There are 2 methods for communicating between the microcontroller and the external system: 1. Polling 2. Interrupt
- 4. What is Interrupt: ► A signal to the CPU to take an immediate action is called an interrupt. Thus, interrupt is a process with the help of which the CPU is notified of requiring attention. The interrupt is considered as a hardware mechanism. The interrupt requires the operating system to stop and figure out what to do next.
- 5. What is Polling :- ► The process in which the CPU constantly checks the status of the device- to see if it needs the CPU's attention is called polling. It is basically a protocol in which the CPU services the I/O devices. Thus, the polling is the process of periodically checking status of a device to see if it is time for the next I/O operation.
- 6. Interrupt Vs Polling Interrupt Polling An interrupt is a process with the help of which the CPU is notified of requiring attention. Polling is the process in which the CPU constantly checks the status of a device to see if it needs the CPU's attention. It is considered as a hardware mechanism. It is a protocol. An interrupt handler services/works with the device. In this protocol, the CPU services the device. Interrupt-request line indicates that the device needs to be serviced. The command-ready bit indicates that the device needs to be serviced. An interrupt handler services/works with the device. In this protocol, the CPU services the device. Interrupt-request line indicates that the device needs to be serviced. The command-ready bit indicates that the device needs to be serviced. CPU is used only when a device requires servicing. CPU is used only when a device requires servicing. Interrupts save the CPU cycles. Polling wastes many of the CPU cycles. Interrupts can occur at any point in time. CPU polls the devices at regular intervals of time. It becomes inefficient if devices frequently interrupt the CPU. Polling becomes inefficient when the CPU rarely finds a device that is ready to be serviced.
- 7. Steps in executing an interrupt •Upon activation of interrupt the microcontroller • Finishes executing the current instruction • Store next instruction address in PC & current status in stack memory. • Processor Jumps to the interrupt vector table(IVT) to get the address of ISR and jumps to it • Transfer program control to the ISR • Begin executing the ISR instructions to the last instruction of ISR (RETFIF) • Executes RETFIE • Pops the PC from the stack • Starts to execute from the address of that PC 11-9
- 8. Classification of Interrupts •Maskable Interrupts •Nonmaskable Interrupts •Vectored Interrupts •Non-vectored Interrupts
- 9. Note: Non Maskable : cannot be disabled or ignored by the instructions of CPU Maskable : disabled or ignored by the instructions of CPU
- 11. Sources of Interrupts: ► External hardware interrupts : INT0, INT1 AND INT2 ► Timer Interrupts : TMR0IF, TMR1IF, TMR2IF AND TMR3IF ► Serial communication interrupts : TXIF and RCIF ► RB port change interrupt : RBIF ► A/D converter interrupt : ADIF ► Compare, Capture, PWM interrupt : CCP1IF
- 12. Simplified interrupt structure of PIC 18
- 13. Enabling and Disabling Interrupts GIE PEIE TMR0IE INT0IE RBIE Bit 7 GIE Global Interrupt Enable bit 1 = Enables all unmasked interrupts 0 = Disables all interrupt Bit 6 PEIE Peripheral Interrupt Enable bit 1 = Enable all unmasked peripheral interrupts 0 = Disable all peripheral interrupts Bit 5 TMR0IE TMR0 Overflow Interrupt Enable bit 1 = Enables the TMR0 overflow interrupt 0 = Disables the INT0 overflow interrupt Bit 4 INT0IE INT0 External Interrupt Enable bit 1 = Enables the INT0 external interrupt 0 = Disables the INT0 external interrupt Bit 3 RBIE RB port change Interrupt Enable bit 1 = Enables the RB port change interrupt 0 = Disables the RB port change interrupt
- 14. Interrupt Registers ► For PIC18F458 microcontroller, 13 registers are used to control interrupt operation. These registers are : 1. RCON 2. INTCON 3. INTCON2 4. INTCON3 5. PIR1, PIR2, PIR3 6. PIE1, PIE2, PIE3 7. IPR1, IPR2, IPR3
- 15. RCON Register : Reset control register IPEN SBOREN - R1 TO PD POR BOR IPEN INTERRUPT PRIORITY ENABLE BIT 1= ENABLE PRIORITY LEVELS ON INTERRUPT 0= DISABLE PRIORITY LEVELS ON INTERRUPT SBOREN BOR SOFTWARE ENABLE BIT R1 RESET INSTRUCTION FLAG BIT TO WATCHDOG TIME OUT FLAG BIT PD POWER DOWN DETECTION FLAG BIT POR POWER ON RESET FLAG BIT BOR BROWN OUT RESET STATUS BIT
- 16. INTCON REGISTERS ► The INTCON registers are readable and writable registers that contains various enable, priority and flag bits. Because of the number of interrupts to be controlled, pic18F devices have three INTCON registers. ► 1. INTCON registers ► 2. INTCON2 registers ► 3. INTCON3 registers
- 17. INTCON register:- GIE/GIEH PEIE/GIEL TMR0IE INT0IE RBIE TMR0IF INT0IF RBIF
- 18. GIE/GIEH When IPEN=0, 1=enables all unmasked interrupts 0=disable When IPEN=1, 1=enable all high priority interrupts 0=disable PEIE/GIEL When IPEN=0, 1=enables all unmasked peripheral interrupts 0=disable When IPEN=1, 1=enable all low priority peripheral interrupts 0=disable TMR0IE 1=enable the TMR0 overflow interrupt 0=disable INT0IE 1=enables the INT0 external interrupt 0=disable RBIE 1=enables the RB port change interrupt 0=disable TMR0IF 1=The timer 0 register has overflowed 0=-not overflow INT0IF 1=The INT0 external interrupt occurred 0=disable RBIF 1=At least one of the RB7 : RB4 pins changed state 0=None of the pins changed
- 19. RBPU INTEDG0 INTEDG1 --- --- TMROIP ----- RBIP INTCON2 REGISTER:
- 20. INTCON3 REGISTER: INT2IP INT1IP ---- INT2IE INT1IE ---- INT2IF INT1IF
- 21. INTCON INTCON2 INTCON3 GIE/GIEH PEIE/GIEL TMR0IE INT0IE RBIE TMR0IF INT0IF RBIF RBPU INTEDG0 INTEDG1 --- --- TMROIP ----- RBIP INT2IP INT1IP ---- INT2IE INT1IE ---- INT2IF INT1IF
- 22. Show the instructions to •A. Enable (unmask) the Timer 0 interrupt and external hardware interrupt 0 (INT0) BSF INTCON, TMR0IE; enable Timer 0 Interrupt BSF INTCON, INT0IE ; enable external interrupt BSF INTCON, GIE; allow interrupts to come in
- 23. Show the instructions to B. Disable (mask) the Timer 0 interrupt, then BCF INTCON, TMR0IE ; mask (disable) Timer 0 Interrupt C. Show how to disable (mask) all the interrupts with a single instruction. BCF INTCON,GIE ;mask all interrupts globally
- 24. PIR registers: ► The peripheral Interrupt Request (PIR) register contains the individual flag bits for the peripheral interrupts. ► Due to the number of peripheral interrupt sources, there are three peripheral interrupt request registers (PIR1, PIR2, PIR3)
- 25. PIR1 (Peripheral Interrupt Request Register 1) PSPIF: Parallel Slave Port Read/Write Interrupt Flag bit(1) 1 = A read or a write operation has taken place 0 = No read or write has occurred ADIF: A/D Converter Interrupt Flag bit 1 = An A/D conversion completed 0 = The A/D conversion is not complete RCIF: USART Receive Interrupt Flag bit 1 = The USART receive buffer is full 0 = The USART receive buffer is empty TXIF: USART Transmit Interrupt Flag bit 1 = The USART transmit buffer is empty 0 = The USART transmit buffer is full SSPIF: Synchronous Serial Port (SSP) Interrupt Flag bit CCP1IF: CCP1 Interrupt Flag bit TMR2IF: TMR2 to PR2 Match Interrupt Flag bit 1 = TMR2 to PR2 match occurred 0 = No TMR2 to PR2 match occurred TMR1IF: TMR1 Overflow Interrupt Flag bit 1 = TMR1 register overflowed 0 = TMR1 register did not overflow
- 26. CMIF: Comparator Interrupt Flag bit 1 = The comparator input has changed 0 = The comparator input has not changed EEIF: EEPROM Write Operation Interrupt Flag bit 1 = The write operation completed 0 = The write operation is not complete or has not been started BCLIF: Bus Collision Interrupt Flag bit 1 = A bus collision has occurred in the SSP when configured for I2C Master mode 0 = No bus collision has occurred CCP2IF: CCP2 Interrupt Flag bit PIR2 (Peripheral Interrupt Request Register 2)
- 27. PIR3
- 28. PIE Register (Peripheral Interrupt Enable) ► PIE Register (Peripheral Interrupt Enable) contain the individual enable bits for the peripheral interrupts. ► Due to the number of peripheral interrupt sources, there are three peripheral Interrupt Enable registers (PIE1, PIE2, PIE3) ► When IPEN is clear, the PEIE bit must be set to enable any of these peripheral interrupts.
- 29. PIE Register 1 (Peripheral Interrupt Enable) PSPIE: Parallel Slave Port Read/Write Interrupt Enable bit(1) 1 = Enables the PSP read/write interrupt 0 = Disables the PSP read/write interrupt ADIE: A/D Converter Interrupt Enable bit 1 = Enables the A/D converter interrupt 0 = Disables the A/D converter interrupt RCIE: USART Receive Interrupt Enable bit 1 = Enables the USART to receive interrupt 0 = Disables the USART receive interrupt RCIE: USART Receive Interrupt Enable bit 1 = Enables the USART to receive interrupt 0 = Disables the USART receive interrupt TXIE: USART Transmit Interrupt Enable bit 1 = Enables the USART to transmit interrupt 0 = Disables the USART transmit interrupt SSPIE: Synchronous Serial Port Interrupt Enable bit 1 = Enables the SSP interrupt 0 = Disables the SSP interrupt CCP1IE: CCP1 Interrupt Enable bit 1 = Enables the CCP1 interrupt 0 = Disables the CCP1 interrupt TMR2IE: TMR2 to PR2 Match Interrupt Enable bit 1 = Enables the TMR2 to PR2 match interrupt 0 = Disables the TMR2 to PR2 match interrupt
- 30. CMIE: Comparator Interrupt Enable bit 1 = Enables the comparator interrupt 0 = Disable the comparator interrupt EEIE: EEPROM Write Operation Interrupt Enable bit 1 = Enable EEPROM write interrupt 0 = Disable EEPROM write interrupt BCLIE: Bus Collision Interrupt Enable bit 1 = Enable bus collision interrupt 0 = Disable bus collision interrupt CCP2IE: CCP2 Interrupt Enable bit 1 = Enables the CCP2 interrupt 0 = Disables the CCP2 interrupt
- 31. PIE Register 3 (Peripheral Interrupt Enable) IRXIE WAKIE ERRIE TXB2IE TXB1IE TXB0IE RXB1IE RXB0IE
- 32. IPR (Interrupt Priority Request)
- 33. IPR 1 (Interrupt Priority Request)
- 34. IPR 2 (Interrupt Priority Request)
- 35. IPR 3(Interrupt Priority Request)
- 36. Steps for programming PIC18 timer using Interrupt: 1. Enable GIE,PEIE,TMRxIE 2. Configure the TxCON register 3. Clear TMRxIF Timer interrupt flag. 4. Load the count in Timer register TMRx. 5. Set TMRxON to start Timer operation. 6. When TMRxIF =1 , code will jump to ISR to execute it, and after excecution control returns to the main program.
- 38. Example: Write a C program for the PIC18 to generate a square wave of 2 KHz frequency on RB4 using Timer0 ISR and a square wave of 5 KHz frequency on RB5 using TIMER1 ISR. Assume XTAL=10 MHz Answer : Given : Fosc = 10 MHz , No Prescaler Ftimer =Fosc /4 = 10/4= 2.5 MHz Period = 1/Timer= 1/ 2.5 MHz = 0.4 µsec. For 2 KHz T= 1/2KHz = 0.5 µsec. Ton = Toff = T/2 = .25 µsec. Count = Desired Delay/ Timer Period = .25 µsec./ .4 µsec. = 625 The value to be loaded in 16 bit Timer0 register is : 65536- period Count=65536-625 = 65911 = FD8FH ► For 5KHz T= 1/5KHz = 0.2 µsec. Ton = Toff = T/2 = .1 µsec. Count = Desired Delay/ Timer Period = .1 µsec./ .4 µsec. = 250 The value to be loaded in 16 bit Timer1 register is : 65536-period Count=65536-250 = 65286 = FF06H
- 39. #include<P18F4550.h> void Timer0_ISR(void); void CHK_ISR(void); #define PORTBit1 PORTbits.RB4 #define PORTBit2 PORTbits.RB5 #pragma interrupt CHK_ISR void CHK_ISR(void) { if (INTCONbits.TMR0IF=1) TIMER0_ISR(); if (PIR1bits.TMR1IF=1) TIMER1_ISR(); } #pragma code Void main(void) { TRISBbits.TRISB4=0; configure pin4 port B as o/p TRISBbits.TRISB5=0; configure pin5 port B as o/p INTCONbits.GIE=1; INTCONbits.PEIE=1; TOCON=0x08; timer 0 16 bitmode no prescaler INTCONbits.TMROIF =0; clear timer 0 interrupt flag bit TMR0H=0xFD; load higher byte TMR0L=0X8F; load lower byte INTCONbits.TMR0IE=1; enable timer0 interrupt T1CON=0x08; PIR1bits.TMR1IF =0; TMR1H=0xFF; TMR1L=0X06; PIE1bits.TMR1IE=1; TOCONbits.TMR0ON=1; T1CONbits.TMR1ON=1; While(1); }
- 40. void Timer0_ISR(void) { PORTBit1= ~PORTBit1; TMR0H=0xFD; TMR0L=0x8F; INTCONbits.TMR0IF=0; } void Timer1_ISR(void) { PORTBit2= ~PORTBit2; TMR1H=0xFF; TMR1L=0x06; PIRbits.TMR1IF=0; }
- 41. Interfacing of LED ► Current sinking and sourcing capacities in the PIC18 family is about 25 mA. ► We can drive LED using PORT in 2 ways: 1. Current Sourcing mode 2. Current sinking mode. ► Source current is the ability of the digital output/input port to supply current. Sink current is the ability of the port to receive current. a. LED connected in current source mode b. LED connected in current sink mode
- 42. Q. Write an embedded pic18 c program to flash the LED connected to pin 0 of PORTB Assume that Ton and Toff of LED = 500 msec. #include<pic18f4550.h> #define PortBit PORTbits.RB0 void DELAY(unsigned int); void main(void) { TRISBits.TRISB=0; While(1); { PortBit =1; DELAY(500); PortBit =0; DELAY(500); } } Void DELAY (unsigned int t); { unsigned int I,j; for(i=0; i<t; i++) for(j=0; j<165; j++); }
- 43. Q. Write an embedded pic18 c program to blink the LED connected to PORTC Assume that Ton and Toff of LED = 500 msec. #include<pic18f4550.h> void DELAY(unsigned int); void main(void) { TRISC=0; While(1); { PORTC=0x00; DELAY(500); PORTC=0xFF; DELAY(500); } } void DELAY (unsigned int t); { unsigned int I,j; for(i=0; i<t; i++) for(j=0; j<165; j++); }
- 44. Q. An LED connected to each pin of PORT D. Write a PIC18 C program that will turn each LED from pin D0 to D7. Call a delay module before turning on the next LED #include<pic18f4550.h> #define PD0 PORTDbits.RD0 #define PD1 PORTDbits.RD1 #define PD2 PORTDbits.RD2 #define PD3 PORTDbits.RD3 #define PD4 PORTDbits.RD4 #define PD5 PORTDbits.RD5 #define PD6 PORTDbits.RD6 #define PD7 PORTDbits.RD7 void DELAY(unsigned int); void main(void) { TRISD=0; While(1); { PD0 = 1; DELAY(500); PD1 = 1; DELAY(500); PD2 = 1; DELAY(500); PD3= 1; DELAY(500); PD4 = 1; DELAY(500); PD5 = 1; DELAY(500); PD6 = 1; DELAY(500); PD7 = 1; DELAY(500); } } void DELAY (unsigned int t); { unsigned int I,j; for(i=0; i<t; i++) for(j=0; j<165; j++); }
- 45. Interfacing of LCD:- RD0 RD1 RD2 RD3 RD4 RD5 RD6 RD7 RE0 RE1 RE2 DB0 DB1 DB2 DB3 DB4 DB5 DB6 DB7 RS RW E 16 character * 2 line LCD display module 16 character * 2 line LCD display module PIC18XXX Vcc VEE VSS Vcc VEE VSS
- 46. The three control lines are referred to as EN, RS, and RW. The EN line is called “Enable.” This control line is used to tell the LCD that you are sending it data. To send data to the LCD, your program should make sure this line is low (0) and then set the other two control lines and/or put data on the data bus. When the other lines are completely ready, bring EN high (1) and wait for the minimum amount of time required by the LCD datasheet (this varies from LCD to LCD), and end by bringing it low (0) again. The RS line is the “Register Select” line. When RS is low (0), the data is to be treated as a command or special instruction (such as a clear screen, position cursor, etc.). When RS is high (1), the data being sent is text data which should be displayed on the screen. For example, to display the letter “T” on the screen, you would set RS high. The RW line is the “Read/Write” control line. When RW is low (0), the information on the data bus is being written to the LCD. When RW is high (1), the program is effectively querying (or reading) the LCD. Only one instruction (“Get LCD status”) is a read command.
- 47. Program: #include<PIC18F4550.h> #define LCDData PORTD #define RS PORTBbits.RE0 #define RW PORTBbits.RE1 #define EN PORTBbits.RE2 void LCD (unsigned char, unsigned char); void DELAY (unsigned int); void main (void) { TRISD = 0; TRISE = 0; EN=0; LCD(0x38,0) DELAY(250); LCD(0x0E,0); DELAY(15); LCD(0x01,0); DELAY(15); LCD(0x06,0); DELAY(15); LCD(0x86,0); DELAY(15); LCD(‘W’,1); DELAY(15); LCD(‘E’,1); DELAY(15); LCD(‘L’,1); DELAY(15); LCD(‘C’,1); DELAY(15); LCD(‘O’,1); DELAY(15); LCD(‘M’,1); DELAY(15); LCD(‘E’,1); } void LCD (unsigned char value, unsigned char flag) { LCDdata = value; RS=flag; RW=0; EN=1; DELAY(1); EN=0; } Void DELAY(unsigned int cnt) { Unsigned int I,j; For(i=0; i<cnt; i++) for(j=0;j<165;j++); }
- 48. 4*4 keyboard matrix interfacing with PIC controller
- 49. Interfacing Relay:- PIC 18FXXX #include<PIC18F4550.h> #define PORTBIT PORTBbits.RB0 void main(void) { unsigned int i; TRISBbits.TRISB0=0; PORTBIT=1; DELAY(2000); PORTBIT=0; } void DELAY(unsigned int cnt) { unsigned int i,j; for(i=0; i<cnt; i++) for(j=0; j<165; j++) }