Using Pic18 Interrupts.

Pommie · Dec 1, 2022

I had a 4x4 LED matrix setup using a Pic16F873A and swapped the chip to a (same pinout) Pic18F2620. I wanted to see how difficult it would be to run the matrix completely on interrupts.

I setup a 5mS interrupt using Timer 2.

Code:

    //setup 5mS interrupt = 8,000,000/16 = 500,000/10 = 50,000 set PR2=249 = 200 = 5mS 
    T2CON=0b01001110;       //pre=16 post=10
    PR2=249;
    TMR2IE=1;               //timer2 interrupts enable
    GIE=1;
    PEIE=1;

And an ISR to multiplex the LED - stored in a 16 bit variable called LEDs

Code:

//row 0 is RC7 (to RC4) and Anode (+)
//col 0 is RC0 (to RC3) and Cathode (-)
void  __interrupt(high_priority) myHighIsr(void){
    if(TMR2IE && TMR2IF){
        uint16_t temp=LEDs;     //make copy of LED variable
        col++;                  //increment column 
        col&=3;                 //and wrap around to zero
        temp<<=(col*4);         //get 4 LEDs in top bits
        temp&=0xf000;           //get rid of unwanted LEDs
        temp>>=8;               //shift to bits 4 to 7
        temp|=(0x0f-(1<<col));  //turn off unwanted columns
        LATC|=0x0f;             //turn all columns off
        LATC=(uint8_t)temp;     //turn on relevant LEDs
        TMR2IF=0;
    }
}

In the main lood I did a simple scrolling LED routine,

Code:

    while (1){
        __delay_ms(50);         //short delay
        if(dir) LEDs>>=1;       //if dir = 1 then move right
        else LEDs<<=1;          //else move left
        if(LEDs&1) dir=0;       //if we reached the right end then go left
        if(LEDs&0x8000) dir=1;  //if we reached the left end then go right
    }

And this is what it looked like,

Here's the complete code for anyone wanting to know about interrupts. The config statements are longer than the actual code!!!

Code:

// CONFIG1H
#pragma config OSC = INTIO67    // Oscillator Selection bits (Internal oscillator block, port function on RA6 and RA7)
#pragma config FCMEN = ON       // Fail-Safe Clock Monitor Enable bit (Fail-Safe Clock Monitor enabled)
#pragma config IESO = ON        // Internal/External Oscillator Switchover bit (Oscillator Switchover mode enabled)

// CONFIG2L
#pragma config PWRT = ON        // Power-up Timer Enable bit (PWRT enabled)
#pragma config BOREN = SBORDIS  // Brown-out Reset Enable bits (Brown-out Reset enabled in hardware only (SBOREN is disabled))
#pragma config BORV = 3         // Brown Out Reset Voltage bits (Minimum setting)

// CONFIG2H
#pragma config WDT = OFF        // Watchdog Timer Enable bit (WDT enabled)
#pragma config WDTPS = 32768    // Watchdog Timer Postscale Select bits (1:32768)

// CONFIG3H
#pragma config CCP2MX = PORTC   // CCP2 MUX bit (CCP2 input/output is multiplexed with RC1)
#pragma config PBADEN = ON      // PORTB A/D Enable bit (PORTB<4:0> pins are configured as analog input channels on Reset)
#pragma config LPT1OSC = OFF    // Low-Power Timer1 Oscillator Enable bit (Timer1 configured for higher power operation)
#pragma config MCLRE = ON       // MCLR Pin Enable bit (MCLR pin enabled; RE3 input pin disabled)

// CONFIG4L
#pragma config STVREN = ON      // Stack Full/Underflow Reset Enable bit (Stack full/underflow will cause Reset)
#pragma config LVP = OFF        // Single-Supply ICSP Enable bit (Single-Supply ICSP enabled)
#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 bit (Block 0 (000800-003FFFh) not code-protected)
#pragma config CP1 = OFF        // Code Protection bit (Block 1 (004000-007FFFh) not code-protected)
#pragma config CP2 = OFF        // Code Protection bit (Block 2 (008000-00BFFFh) not code-protected)
#pragma config CP3 = OFF        // Code Protection bit (Block 3 (00C000-00FFFFh) 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 bit (Block 0 (000800-003FFFh) not write-protected)
#pragma config WRT1 = OFF       // Write Protection bit (Block 1 (004000-007FFFh) not write-protected)
#pragma config WRT2 = OFF       // Write Protection bit (Block 2 (008000-00BFFFh) not write-protected)
#pragma config WRT3 = OFF       // Write Protection bit (Block 3 (00C000-00FFFFh) 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 bit (Block 0 (000800-003FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR1 = OFF      // Table Read Protection bit (Block 1 (004000-007FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR2 = OFF      // Table Read Protection bit (Block 2 (008000-00BFFFh) not protected from table reads executed in other blocks)
#pragma config EBTR3 = OFF      // Table Read Protection bit (Block 3 (00C000-00FFFFh) 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)

#include <xc.h>
#include <stdint.h>
#define _XTAL_FREQ 32000000

volatile uint8_t col=0,dir;
uint16_t LEDs;

//row 0 is RC7 (to RC4) and Anode (+)
//col 0 is RC0 (to RC3) and Cathode (-)
void  __interrupt(high_priority) myHighIsr(void){
    if(TMR2IE && TMR2IF){
        uint16_t temp=LEDs;     //make copy of LED variable
        col++;                  //increment column 
        col&=3;                 //and wrap around to zero
        temp<<=(col*4);         //get 4 LEDs in top bits
        temp&=0xf000;           //get rid of unwanted LEDs
        temp>>=8;               //shift to bits 4 to 7
        temp|=(0x0f-(1<<col));  //turn off unwanted columns
        LATC|=0x0f;             //turn all columns off
        LATC=(uint8_t)temp;     //turn on relevant LEDs
        TMR2IF=0;
    }
}

void main(void){
    OSCCON=0b01110000;      //8MHz
    PLLEN=1;                //x4=32MHz
    //setup 5mS interrupt = 8,000,000/16 = 500,000/10 = 50,000 set PR2=249 = 200 = 5mS 
    T2CON=0b01001110;       //pre=16 post=10
    PR2=249;
    TMR2IE=1;               //timer2 interrupts enable
    GIE=1;
    PEIE=1;
    TRISC=0;                //all output
    LEDs=0xf000;
    dir=1;
    while (1){
        __delay_ms(50);         //short delay
        if(dir) LEDs>>=1;       //if dir = 1 then move right
        else LEDs<<=1;          //else move left
        if(LEDs&1) dir=0;       //if we reached the right end then go left
        if(LEDs&0x8000) dir=1;  //if we reached the left end then go right
    }
}

Mike.
A question for knowledgeable people,
The two instructions

Code:

        col++;                  //increment column 
        col&=3;                 //and wrap around to zero

Can't be combined into

Code:

        ++col&=3;

I can't think why it isn't permitted. There must be a simple reason that I'm not seeing.

Ian Rogers · Dec 2, 2022

It's all to with the increment precedence. I agree but just make a small program and put both in, then look at the asm produced to see if it works.

Ian Rogers · Dec 2, 2022

Scratch that doesn't even compile..

tumbleweed · Dec 2, 2022

Code:

 ++col &= 3;

The error that generates is "error: (202) only lvalues can be assigned to or modified"

'lvalue' means an object that has a location in memory (i.e. it has an address).
An lvalue cannot be a function, an expression (like ++col) or a constant (like 3 , 4 , etc.).

Ian Rogers · Dec 2, 2022

I think the compiler see's the ++col then immeadiately finds '&' and is now an "address of"..

Pommie · Dec 2, 2022

Interestingly,

Code:

  col=++col&3;

only produces a warning,
main.c:71:13: warning: multiple unsequenced modifications to 'col' [-Wunsequenced]
I don't even know what that is warning about.
What's an "unsequenced" modification?

Mike.

tumbleweed · Dec 2, 2022

It's warning you that the result is unspecified and may not be what you expect.

Statements like

Code:

col = ++col;

produce undefined behavior. It all has to do with "sequence points" and the language spec..

Pommie · Dec 2, 2022

I thought precedence took care of that with ++ having a precedence of 2 and &= a precedence of 14.

I don't understand how there can be undefined behaviour.

Mike.

tumbleweed · Dec 3, 2022

oogle
"c increment operator multiple unsequenced modifications" and/or "c increment operator undefined behavior" for lengthy discussions from the language lawyers.

Mike - K8LH · Dec 3, 2022

Mike. Please forgive me. I can't help myself. I always wonder how I might do things differently (not necessarily better)...

Code:

  void  __interrupt(high_priority) myHighIsr(void)
  { static uint8_t col = 8;          // value; 1, 2, 4, 8
    static uint16_t temp = 0;        //
    if(TMR2IE && TMR2IF)
    { LATC = col ^ 0x0F;             // display off, select column
      LATC |= (hi(temp) & 0xF0);     // display new column
      col <<= 1; temp <<= 4;         // prep for next column
      if(col & 16)                   // if last column
      { col = 1;                     //   reset 'column'
        temp = led;                  //   refresh 'temp'
      }                              //
      TMR2IF = 0;                    //
    }                                //
  }                                  //

And <off topic>, I know, but, have you ever done anything with Charlieplexing?

Happy Holidays. Cheerful regards, Mike

Pommie · Dec 3, 2022

Ahhh, I see the equals and the increment are both modifying it, hence confusion.

It also explains why col=col+1&3 works (+ is higher precedence).

I still think precedence takes away the unsequenced part as precedence gives it sequence - increment first then AND and assign. Made me think, is equals given a precedent? Yes it is, it's assigned 14 the lowest.
I'm trying to get my head around why e = a < d ? a++ : a = d can't be parsed.

Mike, yes, I've used charlieplexing many times in the past. If you remember, I used it to read a 4x3 keyboard using just 5 pins - keeping one pin free (of an 8 pin pic) to transmit RS232.

Mike.

Mike - K8LH · Dec 3, 2022

Pommie said:
... If you remember, I used it to read a 4x3 keyboard using just 5 pins - keeping one pin free (of an 8 pin pic) to transmit RS232.

I don't remember that one specifically. Will have to search for it.

Happy Holidays.

Pommie · Dec 3, 2022

Nope, 3 pins with 200k pulldowns that could be pulled up internally (20k) for the (3) columns. Four diodes feeding the (4) rows - two each way. It's on here somewhere. The free pin was a 6th pin used to send the results via RS232.

Found it but it appears the original article has been deleted. https://www.electro-tech-online.com...autorepeat-and-2-key-rollover-deleted.138170/

Mike.

Pommie · Dec 3, 2022

Was trying to remember how I did this all those years ago. Turns out GP0, 1 & 3 have WPUs so these were the column inputs. GP2 and 4 went to the 4 rows via diodes (2 one way, two reversed). So no WPUs on columns float low unless pulled high by the rows via a switch. WPUs on columns float high unless pulled low ......

Mike.

tepalia02 · Dec 4, 2022

Pommie said:

I had a 4x4 LED matrix setup using a Pic16F873A and swapped the chip to a (same pinout) Pic18F2620. I wanted to see how difficult it would be to run the matrix completely on interrupts.

I setup a 5mS interrupt using Timer 2.

Code:

    //setup 5mS interrupt = 8,000,000/16 = 500,000/10 = 50,000 set PR2=249 = 200 = 5mS
    T2CON=0b01001110;       //pre=16 post=10
    PR2=249;
    TMR2IE=1;               //timer2 interrupts enable
    GIE=1;
    PEIE=1;

And an ISR to multiplex the LED - stored in a 16 bit variable called LEDs

Code:

//row 0 is RC7 (to RC4) and Anode (+)
//col 0 is RC0 (to RC3) and Cathode (-)
void  __interrupt(high_priority) myHighIsr(void){
    if(TMR2IE && TMR2IF){
        uint16_t temp=LEDs;     //make copy of LED variable
        col++;                  //increment column
        col&=3;                 //and wrap around to zero
        temp<<=(col*4);         //get 4 LEDs in top bits
        temp&=0xf000;           //get rid of unwanted LEDs
        temp>>=8;               //shift to bits 4 to 7
        temp|=(0x0f-(1<<col));  //turn off unwanted columns
        LATC|=0x0f;             //turn all columns off
        LATC=(uint8_t)temp;     //turn on relevant LEDs
        TMR2IF=0;
    }
}

In the main lood I did a simple scrolling LED routine,

Code:

    while (1){
        __delay_ms(50);         //short delay
        if(dir) LEDs>>=1;       //if dir = 1 then move right
        else LEDs<<=1;          //else move left
        if(LEDs&1) dir=0;       //if we reached the right end then go left
        if(LEDs&0x8000) dir=1;  //if we reached the left end then go right
    }

And this is what it looked like,

Here's the complete code for anyone wanting to know about interrupts. The config statements are longer than the actual code!!!

Code:

// CONFIG1H
#pragma config OSC = INTIO67    // Oscillator Selection bits (Internal oscillator block, port function on RA6 and RA7)
#pragma config FCMEN = ON       // Fail-Safe Clock Monitor Enable bit (Fail-Safe Clock Monitor enabled)
#pragma config IESO = ON        // Internal/External Oscillator Switchover bit (Oscillator Switchover mode enabled)

// CONFIG2L
#pragma config PWRT = ON        // Power-up Timer Enable bit (PWRT enabled)
#pragma config BOREN = SBORDIS  // Brown-out Reset Enable bits (Brown-out Reset enabled in hardware only (SBOREN is disabled))
#pragma config BORV = 3         // Brown Out Reset Voltage bits (Minimum setting)

// CONFIG2H
#pragma config WDT = OFF        // Watchdog Timer Enable bit (WDT enabled)
#pragma config WDTPS = 32768    // Watchdog Timer Postscale Select bits (1:32768)

// CONFIG3H
#pragma config CCP2MX = PORTC   // CCP2 MUX bit (CCP2 input/output is multiplexed with RC1)
#pragma config PBADEN = ON      // PORTB A/D Enable bit (PORTB<4:0> pins are configured as analog input channels on Reset)
#pragma config LPT1OSC = OFF    // Low-Power Timer1 Oscillator Enable bit (Timer1 configured for higher power operation)
#pragma config MCLRE = ON       // MCLR Pin Enable bit (MCLR pin enabled; RE3 input pin disabled)

// CONFIG4L
#pragma config STVREN = ON      // Stack Full/Underflow Reset Enable bit (Stack full/underflow will cause Reset)
#pragma config LVP = OFF        // Single-Supply ICSP Enable bit (Single-Supply ICSP enabled)
#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 bit (Block 0 (000800-003FFFh) not code-protected)
#pragma config CP1 = OFF        // Code Protection bit (Block 1 (004000-007FFFh) not code-protected)
#pragma config CP2 = OFF        // Code Protection bit (Block 2 (008000-00BFFFh) not code-protected)
#pragma config CP3 = OFF        // Code Protection bit (Block 3 (00C000-00FFFFh) 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 bit (Block 0 (000800-003FFFh) not write-protected)
#pragma config WRT1 = OFF       // Write Protection bit (Block 1 (004000-007FFFh) not write-protected)
#pragma config WRT2 = OFF       // Write Protection bit (Block 2 (008000-00BFFFh) not write-protected)
#pragma config WRT3 = OFF       // Write Protection bit (Block 3 (00C000-00FFFFh) 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 bit (Block 0 (000800-003FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR1 = OFF      // Table Read Protection bit (Block 1 (004000-007FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR2 = OFF      // Table Read Protection bit (Block 2 (008000-00BFFFh) not protected from table reads executed in other blocks)
#pragma config EBTR3 = OFF      // Table Read Protection bit (Block 3 (00C000-00FFFFh) 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)

#include <xc.h>
#include <stdint.h>
#define _XTAL_FREQ 32000000

volatile uint8_t col=0,dir;
uint16_t LEDs;

//row 0 is RC7 (to RC4) and Anode (+)
//col 0 is RC0 (to RC3) and Cathode (-)
void  __interrupt(high_priority) myHighIsr(void){
    if(TMR2IE && TMR2IF){
        uint16_t temp=LEDs;     //make copy of LED variable
        col++;                  //increment column
        col&=3;                 //and wrap around to zero
        temp<<=(col*4);         //get 4 LEDs in top bits
        temp&=0xf000;           //get rid of unwanted LEDs
        temp>>=8;               //shift to bits 4 to 7
        temp|=(0x0f-(1<<col));  //turn off unwanted columns
        LATC|=0x0f;             //turn all columns off
        LATC=(uint8_t)temp;     //turn on relevant LEDs
        TMR2IF=0;
    }
}

void main(void){
    OSCCON=0b01110000;      //8MHz
    PLLEN=1;                //x4=32MHz
    //setup 5mS interrupt = 8,000,000/16 = 500,000/10 = 50,000 set PR2=249 = 200 = 5mS
    T2CON=0b01001110;       //pre=16 post=10
    PR2=249;
    TMR2IE=1;               //timer2 interrupts enable
    GIE=1;
    PEIE=1;
    TRISC=0;                //all output
    LEDs=0xf000;
    dir=1;
    while (1){
        __delay_ms(50);         //short delay
        if(dir) LEDs>>=1;       //if dir = 1 then move right
        else LEDs<<=1;          //else move left
        if(LEDs&1) dir=0;       //if we reached the right end then go left
        if(LEDs&0x8000) dir=1;  //if we reached the left end then go right
    }
}

Mike.
A question for knowledgeable people,
The two instructions

Code:

        col++;                  //increment column
        col&=3;                 //and wrap around to zero

Can't be combined into

Code:

        ++col&=3;

I can't think why it isn't permitted. There must be a simple reason that I'm not seeing.

Off topic question: what compiler did you use here to write this code?

Pommie · Dec 4, 2022

It's MPLABX (spit spit) with XC8.

Mike.

Using Pic18 Interrupts.

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