Editing PIC microcontrollers (section)

===Data space (RAM)===
PICs have a set of registers that function as general-purpose RAM. Special-purpose control registers for on-chip hardware resources are also mapped into the data space. The addressability of memory varies depending on device series, and all PIC device types have some [[Bank switching|banking mechanism]] to extend addressing to additional memory (but some device models have only one bank implemented). Later series of devices feature move instructions, which can cover the whole addressable space, independent of the selected bank. In earlier devices, any register move must be achieved through the accumulator.

To implement indirect addressing, a "file select register" (FSR) and "indirect register" (INDF) are used. A register number is written to the FSR, after which reads from or writes to INDF will actually be from or to the register pointed to by FSR. Later devices extended this concept with post- and pre- increment/decrement for greater efficiency in accessing sequentially stored data. This also allows FSR to be treated almost like a stack pointer (SP).

External data memory is not directly addressable except in some PIC18 devices with high pin count. However, general I/O ports can be used to implement a parallel bus or a serial interface for accessing external memory and other peripherals (using subroutines), with the caveat that such programmed memory access is (of course) much slower than access to the native memory of the PIC MCU.