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 Figure 1-1), and under the XC8 Linker categories tab, fill in the information as shown below:
    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
    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
  2. 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