What happens at System Start-up (RESET)

There are several sources of a RESET on the enhanced mid-range PIC MCU. The RESET sources common to almost all applications are the Power-On Reset (POR) and Brown-Out Reset (BOR) due to a sagging power supply voltage (i.e., brown-out). There are several other methods for resetting the MCU including Watchdog timeout and directly accessing the external MCLR pin.

Program Counter is Set to 0x00

After a RESET the instruction located at address 0 is the first instruction executed. The application developer is responsible for placing code into this address to "boot up" the PIC. Microchip's MPLAB XC8 compiler inserts the appropriate instructions to start-up the PIC and transfers control to main. Assembly level programmers have to write the code to initialize the PIC and jump past the Interrupt Vector located at address 0x04.

All Special Function Registers are Set to a Default Value

The datasheet for each enhanced mid-range PIC MCU shows the values which the registers contain at RESET.