Editing PIC microcontrollers (section)

===Limitations===
* One [[Accumulator (computing)|accumulator]]
* Register-[[bank switching]] is required to access the entire RAM of many devices
* Operations and registers are not [[Orthogonal#Computer science|orthogonal]]; some instructions can address RAM and/or [[constant (computer science)|immediate]] constants, while others can use the accumulator only.

The following stack limitations have been addressed in the '''PIC18''' series, but still apply to earlier cores:

* The hardware call stack is not addressable, so preemptive [[computer multitasking|task switching]] cannot be implemented
* Software-implemented [[stack (data structure)|stack]]s are not efficient, so it is difficult to generate [[Reentrant (subroutine)|reentrant]] code and support [[local variable]]s

With paged program memory, there are two page sizes to worry about: one for CALL and GOTO and another for computed GOTO (typically used for table lookups). For example, on PIC16, CALL and GOTO have 11 bits of addressing, so the page size is 2048 instruction words. For computed GOTOs, where you add to PCL, the page size is 256 instruction words. In both cases, the upper address bits are provided by the PCLATH register. This register must be changed every time control transfers between pages. PCLATH must also be preserved by any interrupt handler.<ref>{{cite web|url=http://massmind.org/techref/microchip/pages.htm|title=Slowing 208.80.153.50,10-192-48-43&c=1&t=43197.5553483796|website=massmind.org|access-date=7 April 2018}}</ref>