Is there a memory limitation to write a low priority service

Is there a memory limitation to write a low priority service routine starting at the memory location 00018H?

Solution

Yes there is a memory limitation to write a low priority service routine starting at the memory location 00018H. In the PIC18 Microcontroller, the program memory organization contains the program counter (PC) which is a 21 bit long. It enables the user program to access up to 2 MB of program memory. The PIC18 has a 31-entry return address stack to hold the return address for subroutine call. After power-on, the PIC18 starts to execute instructions from address 0. The location at address 0x08 is reserved for high-priority interrupt service routine.The location at address 0x18 is reserved for low-priority interrupt service priority interrupt service routine. Up to 128KB (at present time) of program memory is inside the MCU chip. Part of the program memory is located outside of the MCU chip.