1.3.1 The First Instruction Fetch by the CPU Under Certain Conditions Will Fail

The first instruction fetch by the CPU will fail immediately after Power-up, a device Reset, waking up from Sleep, or jumping into an Interrupt Service Routine (ISR). This failure occurs when the device frequency is above 16 MHz (FOSC > 16 MHz).

Work arounds

Option 1: Reduce the device frequency to 16 MHz or below (FOSC ≤ 16 MHz).

Option 2: If the device must operate above 16 MHz:

  1. Open the Project Properties window (see The First Instruction Fetch by the CPU Under Certain Conditions Will Fail).
  2. Under the XC8 Linker categories tab, fill in the information as shown below:
    1. In the Option categories drop-down menu, select Fill Flash Memory:
      • In the Which area to fill field, select Provide Range to fill
      • In the How to fill it field, select Constant or incrementing value
      • In the Constant field, enter 0x0
      • In the Increment/Decrement field, select No Incrementing
      • In the Memory address range field, enter '0x0:0x1
      • In the Additional options field, enter -mdebugger=type, where type is the type of debugger tool used for programming/debugging the device as defined in the table below:
        TypeDebugger selected
        noneNo debugger
        icd2MPLAB® ICD 2
        icd3MPLAB ICD 3
        icd4MPLAB ICD 4
        icd5MPLAB ICD 5
        pickit2PICkit™ 2
        pickit3PICkit 3
        pickit4PICkit 4
        pickit5PICkit 5
        realiceMPLAB REAL ICE™ In-circuit Emulator
        ice4MPLAB ICE 4 In-circuit Emulator
        snapMPLAB Snap
        Figure 1-1. Project Properties "Fill Flash Memory" Option Category Window View
    2. In the Option categories drop-down menu (see Figure 1-2), select Additional options:
      • In the Codeoffset field, enter 1
      • Press the Apply button, then press the OK button
      Figure 1-2. Project Properties "Additional Options" Option Category Window View
  3. Add two NOP() instructions immediately after any SLEEP instruction(s):
    #include "mcc_generated_files/system/system.h"

int main(void)
{
    SYSTEM_Initialize();
    INTERRUPT_GlobalInterruptEnable(); 
    WeatherStation_Initialize();

    while(1)
    {
        if(tmr1_tick == 1)
        {
            WeatherStation_Print();
            tmr1_tick = 0;
        }
        SLEEP();       // Wait for interrupt
        NOP();
        NOP();        // Ensure instruction pre-fetched while sleeping
                           // is safe to execute on awakening
    }    
}

Affected Silicon Revisions

A2A3A4
XX