Proteus Simulation Error: "SCS bits have been set. This feature is not modeled"

Thread Starter

Chandler Timm Doloriel

Joined Apr 5, 2018

I have a problem in simulating interrupt/timer0 code in Proteus using PIC18F4520. It says,
"SCS bits have been set. This feature is not modeled. The model continues to clock itself as before".
Here's the main code:
#include <xc.h>
#include <pic18f4520.h>
#include "osciconbits.h"
#include "stdint.h"
#include "stdbool.h"

uint8_t count = 0;
uint8_t button = 0;
bool button_press = false;

void __interrupt() high_isr(void)
     INTCONbits.GIEH = 0;
     if (INTCONbits.TMR0IF)
         if (button_press)
     INTCONbits.GIEH = 1;

void __interrupt(low_priority) low_isr(void)
    INTCONbits.GIEH = 0;
    INTCONbits.GIEH = 1;

void main(void) {
    OSCCONbits.IRCF =  0x07; //8MHz internal clock
    OSCCONbits.SCS =  0x03; //choose internal clock
    TRISBbits.RB6 = 0;
    TRISBbits.RB7 = 0;
    TRISBbits.RB1 = 1;
    LATBbits.LB6 = 0;
    LATBbits.LB7 = 0;
    T0CONbits.TMR0ON = 0;
    T0CONbits.T08BIT = 1;
    T0CONbits.T0CS = 0;
    T0CONbits.PSA = 0;
    T0CONbits.T0PS = 2; //1:8 prescaler
    RCONbits.IPEN = 1;
    INTCONbits.TMR0IE = 1;
    INTCON2bits.TMR0IP = 1;
    INTCONbits.GIEH = 1;
    INTCONbits.GIEL = 1;
    T0CONbits.TMR0ON = 1;
        if (count >= 200)
                LATBbits.LB7 = ~LATBbits.LB7;
                count = 0;
        if (!button_press)
            if (PORTBbits.RB1)
                button_press = true;
        if (button_press)
            if (button >= 40)
                if (PORTBbits.RB1)
                    LATBbits.LB6 = ~LATBbits.LB6;
                    button_press = false;
                    button = 0;
                    button_press = false;
                    button = 0;
and here's the configuration bits:


#include <xc.h> // include processor files - each processor file is guarded.
#define _XTAL_FREQ 8000000
// PIC18F4520 Configuration Bit Settings

// 'C' source line config statements

#pragma config OSC = INTIO67    // Oscillator Selection bits (Internal oscillator block, port function on RA6 and RA7)
#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)

#pragma config PWRT = OFF       // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = OFF      // Brown-out Reset Enable bits (Brown-out Reset disabled in hardware and software)
#pragma config BORV = 3         // Brown Out Reset Voltage bits (Minimum setting)

#pragma config WDT = OFF        // Watchdog Timer Enable bit (WDT disabled (control is placed on the SWDTEN bit))
#pragma config WDTPS = 32768    // Watchdog Timer Postscale Select bits (1:32768)

#pragma config CCP2MX = PORTC   // CCP2 MUX bit (CCP2 input/output is multiplexed with RC1)
#pragma config PBADEN = OFF     // PORTB A/D Enable bit (PORTB<4:0> pins are configured as digital I/O 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)

#pragma config STVREN = ON      // Stack Full/Underflow Reset Enable bit (Stack full/underflow will cause Reset)
#pragma config LVP = ON         // 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))

#pragma config CP0 = OFF        // Code Protection bit (Block 0 (000800-001FFFh) not code-protected)
#pragma config CP1 = OFF        // Code Protection bit (Block 1 (002000-003FFFh) not code-protected)
#pragma config CP2 = OFF        // Code Protection bit (Block 2 (004000-005FFFh) not code-protected)
#pragma config CP3 = OFF        // Code Protection bit (Block 3 (006000-007FFFh) not code-protected)

#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)

#pragma config WRT0 = OFF       // Write Protection bit (Block 0 (000800-001FFFh) not write-protected)
#pragma config WRT1 = OFF       // Write Protection bit (Block 1 (002000-003FFFh) not write-protected)
#pragma config WRT2 = OFF       // Write Protection bit (Block 2 (004000-005FFFh) not write-protected)
#pragma config WRT3 = OFF       // Write Protection bit (Block 3 (006000-007FFFh) not write-protected)

#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)

#pragma config EBTR0 = OFF      // Table Read Protection bit (Block 0 (000800-001FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR1 = OFF      // Table Read Protection bit (Block 1 (002000-003FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR2 = OFF      // Table Read Protection bit (Block 2 (004000-005FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR3 = OFF      // Table Read Protection bit (Block 3 (006000-007FFFh) not protected from table reads executed in other blocks)

#pragma config EBTRB = OFF      // Boot Block Table Read Protection bit (Boot block (000000-0007FFh) not protected from table reads executed in other blocks)

// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.

#endif    /* XC_HEADER_TEMPLATE_H */
And here's the circuit configuration:

(disregard the push-button connection, I have corrected that)

The functionality of the code is to blink the RB7 periodically and turn on the RB6 if the push-button is pressed. Debouncing is added to the code for the button pressing. But the simulation fails and no LED's are turning on, this is the error/warning message I'm getting:


Hope someone can answer this. Thanks!


PS. I have tried removing the GIEH = 1 in interrupt function but the result error is still the same.


Joined Jun 26, 2012
A few things.
  • You must NEVER manually set GIEH or GIEL in an interrupt routine. The stack overflow you see is due to that. The compiler will generate a RETFIE instruction at the end of the interrupt routine to reenable the interrupt AFTER returning to the main routine. The stack is restored before another interrupt can happen.
  • You must clear TOIF in the timer interrupt routine. If you don't it will interrupt again immediately after returning to the main routine.
  • You enable the low priority interrupt but do not have any service routine for low priority interrupts. Do not enable GIEL until you have a service routine.
  • You should not enable any interrupts until you have EVERYTHING fully configured. You are enabling the TIMER0 interrupt before setting its priority. As it happens, default priorities are to the HIGH PRIORITY but if you were setting up a low priority interrupt, it could go to the wrong service routine.
  • I had to comment out the line: while(OSCCONbits.IOFS!=1); to make the simulator run past it. I don't know how Proteus handles that.
  • Microchip recommends that you do not set TRIS bits individually. Write a byte constant to TRISx instead. There are good reasons for this.
  • Proteus objects to the SCSx setting because it doesn't simulate that. Use a default clock to get going.

I am not sure what you are trying to do but good programming practice says you shouldn't process button_press in both an interrupt routine and the main routine. Choose one or the other.

With the GIEH/L stuff removed, clearing T0IF, and the OSCCON IOFS line commented out, it simulated OK in MPLABX

Hope that helps.