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  1. #1
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    PIC18f45k22 UART receive

    Hi frnds

    I have doubt in USART1 Receive PIC18f45k22 controller. I am using C18 compiler. Could you please explain the interrupt vector and isr function.?

    Code:
    #include 
    #include 
    #include 
    #include 
    #include 
    #include 
    
    #define EAUSART_V11
    // CONFIG1H
    #pragma config FOSC = HSMP      // Oscillator Selection bits (HS oscillator (medium power 4-16 MHz))
    #pragma config PLLCFG = OFF     // 4X PLL Enable (Oscillator used directly)
    #pragma config PRICLKEN = OFF   // Primary clock enable bit (Primary clock can be disabled by software)
    #pragma config FCMEN = OFF      // Fail-Safe Clock Monitor Enable bit (Fail-Safe Clock Monitor disabled)
    #pragma config IESO = OFF       // Internal/External Oscillator Switchover bit (Oscillator Switchover mode disabled)
    
    // CONFIG2L
    #pragma config PWRTEN = OFF     // Power-up Timer Enable bit (Power up timer disabled)
    #pragma config BOREN = SBORDIS  // Brown-out Reset Enable bits (Brown-out Reset enabled in hardware only (SBOREN is disabled))
    #pragma config BORV = 190       // Brown Out Reset Voltage bits (VBOR set to 1.90 V nominal)
    
    // CONFIG2H
    #pragma config WDTEN = OFF      // Watchdog Timer Enable bits (Watch dog timer is always disabled. SWDTEN has no effect.)
    #pragma config WDTPS = 1        // Watchdog Timer Postscale Select bits (1:1)
    
    // CONFIG3H
    #pragma config CCP2MX = PORTB3  // CCP2 MUX bit (CCP2 input/output is multiplexed with RB3)
    #pragma config PBADEN = OFF     // PORTB A/D Enable bit (PORTB<5:0> pins are configured as digital I/O on Reset)
    #pragma config CCP3MX = PORTE0  // P3A/CCP3 Mux bit (P3A/CCP3 input/output is mulitplexed with RE0)
    #pragma config HFOFST = OFF     // HFINTOSC Fast Start-up (HFINTOSC output and ready status are delayed by the oscillator stable status)
    #pragma config T3CMX = PORTC0   // Timer3 Clock input mux bit (T3CKI is on RC0)
    #pragma config P2BMX = PORTD2   // ECCP2 B output mux bit (P2B is on RD2)
    #pragma config MCLRE = EXTMCLR  // MCLR Pin Enable bit (MCLR pin enabled, RE3 input pin disabled)
    
    // CONFIG4L
    #pragma config STVREN = OFF     // Stack Full/Underflow Reset Enable bit (Stack full/underflow will not cause Reset)
    #pragma config LVP = OFF        // Single-Supply ICSP Enable bit (Single-Supply ICSP disabled)
    #pragma config XINST = OFF      // Extended Instruction Set Enable bit (Instruction set extension and Indexed Addressing mode disabled (Legacy mode))
    
    // CONFIG5L
    #pragma config CP0 = OFF        // Code Protection Block 0 (Block 0 (000800-001FFFh) not code-protected)
    #pragma config CP1 = OFF        // Code Protection Block 1 (Block 1 (002000-003FFFh) not code-protected)
    #pragma config CP2 = OFF        // Code Protection Block 2 (Block 2 (004000-005FFFh) not code-protected)
    #pragma config CP3 = OFF        // Code Protection Block 3 (Block 3 (006000-007FFFh) not code-protected)
    
    // CONFIG5H
    #pragma config CPB = OFF        // Boot Block Code Protection bit (Boot block (000000-0007FFh) not code-protected)
    #pragma config CPD = OFF        // Data EEPROM Code Protection bit (Data EEPROM not code-protected)
    
    // CONFIG6L
    #pragma config WRT0 = OFF       // Write Protection Block 0 (Block 0 (000800-001FFFh) not write-protected)
    #pragma config WRT1 = OFF       // Write Protection Block 1 (Block 1 (002000-003FFFh) not write-protected)
    #pragma config WRT2 = OFF       // Write Protection Block 2 (Block 2 (004000-005FFFh) not write-protected)
    #pragma config WRT3 = OFF       // Write Protection Block 3 (Block 3 (006000-007FFFh) not write-protected)
    
    // CONFIG6H
    #pragma config WRTC = OFF       // Configuration Register Write Protection bit (Configuration registers (300000-3000FFh) not write-protected)
    #pragma config WRTB = OFF       // Boot Block Write Protection bit (Boot Block (000000-0007FFh) not write-protected)
    #pragma config WRTD = OFF       // Data EEPROM Write Protection bit (Data EEPROM not write-protected)
    
    // CONFIG7L
    #pragma config EBTR0 = OFF      // Table Read Protection Block 0 (Block 0 (000800-001FFFh) not protected from table reads executed in other blocks)
    #pragma config EBTR1 = OFF      // Table Read Protection Block 1 (Block 1 (002000-003FFFh) not protected from table reads executed in other blocks)
    #pragma config EBTR2 = OFF      // Table Read Protection Block 2 (Block 2 (004000-005FFFh) not protected from table reads executed in other blocks)
    #pragma config EBTR3 = OFF      // Table Read Protection Block 3 (Block 3 (006000-007FFFh) not protected from table reads executed in other blocks)
    
    // CONFIG7H
    #pragma config EBTRB = OFF      // Boot Block Table Read Protection bit (Boot Block (000000-0007FFh) not protected from table reads executed in other blocks)
    //#pragma interrupt resv_isr
    unsigned int uiIcnt;
    unsigned char Recv_Data='s';
    
    void resv_isr()
    {
        if(PIR1bits.RC1IF == 1)
        {
            Recv_Data = Read1USART();
            PIR1bits.RC1IF = 0;
            LATEbits.LATE0 = ~LATEbits.LATE0;
       }
        LATEbits.LATE0 = ~LATEbits.LATE0;
    }
    
    
    void main()
    {
        TRISAbits.TRISA0=0;
        TRISCbits.TRISC4=0;
        TRISCbits.TRISC6=0;
        TRISCbits.TRISC7=1;
        TRISEbits.TRISE1=0;
        PORTCbits.RC4=0;
        PORTEbits.RE1=0;
        PORTCbits.RC7=0;
        CloseADC();
        PMD1=0xff;                  //Peripheral Module disable Register
        PMD2=0x0f;
    
        WDTCONbits.SWDTEN = 0;
        ADCON0bits.ADON = 0;
        OSCCON = 0x00;
        OSCCON2 = 0x00;
        OSCTUNE = 0x00;
        
        /* Enable UART1*/
        Open1USART(USART_TX_INT_OFF & USART_RX_INT_ON & USART_ASYNCH_MODE & USART_EIGHT_BIT & USART_CONT_RX & USART_BRGH_HIGH , 77);
    
        /* Enable UART2*/
        Open2USART(USART_TX_INT_OFF & USART_RX_INT_ON & USART_ASYNCH_MODE &   USART_EIGHT_BIT & USART_CONT_RX & USART_BRGH_HIGH , 77);
    
        Delay100TCYx(100);
    
        baud1USART(BAUD_IDLE_CLK_LOW & BAUD_8_BIT_RATE & BAUD_WAKEUP_OFF & BAUD_AUTO_OFF);
    
        baud2USART(BAUD_IDLE_CLK_LOW & BAUD_8_BIT_RATE & BAUD_WAKEUP_OFF &    BAUD_AUTO_OFF);
    
        RCSTA1bits.CREN     = 1;         // Enable Receiver
        RCSTA1bits.SPEN     = 1;         // Serial Port enable
        RCSTAbits.ADDEN     = 0;         // Disable address detection
        RCSTAbits.RX9       = 0;         // 8 bit data Reception
        BAUDCON1bits.DTRXP  = 0;         // Receiver data not invertered
        BAUDCON1bits.RCIDL  = 1;         // Receiver is Idle
        BAUDCON1bits.WUE    = 0;         // Receiver operating normally
        BAUDCON1bits.BRG16  = 0;         // 8 bit Baud rate enable
        BAUDCON1bits.ABDEN  = 0;         // Auto baud detect disabled
        INTCONbits.GIE      = 1;         // Enable Global Interrupt
        INTCONbits.PEIE     = 1;         // Enable Periperal Interrupt
        RCONbits.IPEN       = 1;         // Enable Interrupt Priority
        IPR1bits.RC1IP      = 1;         // Receive UART1 high Interrupt priority
        IPR3bits.RC2IP      = 1;         // Receive UART2 high Interrupt priority
        PIE1bits.RC1IE      = 1;         // Receive UART1 Interrupt enable
        PIE3bits.RC2IE      = 1;         // Receive UART2 Interrupt enable
        PMD0bits.UART1MD    = 0;         // UART1 Module enabled
        PMD0bits.UART2MD    = 0;         // UART2 Module enabled
    
        Delay100TCYx(100);
        while(1)
        {
            LATEbits.LATE1 = 1;
            Delay10KTCYx(200);
            while (!DataRdy1USART());
            if(DataRdy1USART())
            {
                Recv_Data = Read1USART();
                PIR1bits.RC1IF = 0;
            }
            putc2USART('s');
            Delay10KTCYx(200);
            Write1USART(Recv_Data);
            LATEbits.LATE1 = 0;
            Delay10KTCYx(200);
        }
    }
    Thanks,
    Parthi

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  2. #2
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    Re: PIC18f45k22 UART receive

    The interrupt vector is a fixed address in PIC program memory. There is one for low priority interrupts and one for high priority interrupts. You decide in your design whether priorities are needed and if so, which interrupt has priority over others. The compiler knows to place the ISR at the correct address so it gets called when the interrupt occurs.
    Code:
    void resv_isr()                                       // this is called when the interrupt occurs so the compiler places it at the vector
    {
        if(PIR1bits.RC1IF == 1)                       // checks to see if the USART caused the interrupt
        {
            Recv_Data = Read1USART();           // if it did, get the byte from the USART and store it in 'Recv_Data'
            PIR1bits.RC1IF = 0;                       // then clear the interrupt flag so it is ready for the next data to arrive
            LATEbits.LATE0 = ~LATEbits.LATE0; // toggle bit 0 of PORTE (for reasons better known to you)
       }
        LATEbits.LATE0 = ~LATEbits.LATE0;     // toggle bit 0 of PORTE (for reasons better known to you)
    }
    I'm not sure why you toggle PORTE once if something else caused the interrupt and twice if it was the USART or what that port is connected to. If you have OTHER interrupt sources as well, you would add a similar check of the PIR bits to see which was set and perform a similar but appropriate action to your existing code.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


    1 members found this post helpful.

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  3. #3
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    Re: PIC18f45k22 UART receive

    Thanks for reply.

    How to assign Higher priority interrupt?
    But this code is not working. PORTE toggle is used to verify the interrupt working or not.
    Thanks,
    Parthi



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  4. #4
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    Re: PIC18f45k22 UART receive

    Before explaining, tell us what you have connected to PORTE bit 0 to show the interrupt worked. If the interrupt is NOT from the USART the bit should change state but if it is from the USART it will change then immediately change again so the pulse it produces will only be a few uS long.

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  5. #5
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    Re: PIC18f45k22 UART receive

    Thanks.

    Led connected to PORTE bit 0 pin.
    Thanks,
    Parthi



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  6. #6
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    Re: PIC18f45k22 UART receive

    In that case,:
    Code:
    void resv_isr()
    {
        if(PIR1bits.RC1IF == 1)
        {
            Recv_Data = Read1USART();
            PIR1bits.RC1IF = 0;
            LATEbits.LATE0 = ~LATEbits.LATE0;
       }
        LATEbits.LATE0 = ~LATEbits.LATE0;  <<<<<<< remove this line !!!
    }
    That line toggles the state of PORTE bit 0 every time the interrupt routine runs. If the interrupt is actually caused by the USART it will already have changed state in the line above it so you will be setting it back to its original state. It will happen so quickly that there is no chance you would notice the LED flashing.

    Your other mistake is not using the interrupt properly. When a character arrives in the USART it triggers the interrupt and the routine resv_isr() is called. In that routine you read the data from the USART, that is exactly what you should do, but in the main part of the program you try to read it again. What you need is a 'flag' (a bit or variable) inside the ISR that the main routine can use to see if the interrupt has ocurred and therefore that the Recv_Data variable holds the received byte.

    I suggest you add a line in the ISR something like "UsartDataAvailable = 1" then in the main routine, instead of checking
    Code:
            while (!DataRdy1USART());
            if(DataRdy1USART())
            {
                Recv_Data = Read1USART();
                PIR1bits.RC1IF = 0;
            }
    check if UsartDataAvailable == 1 and then you know Recv_Data holds the received byte already. When you have dealt with the byte, use UsartDataAvailable = 0 to reset it for next time. I do not recommend you reset the RCIF bit in your main program loop, it can lose you incoming data.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



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