Modified Harvard architecture 8-bit RISC microcontroller. Atmel's AVRs have a two-stage, single-level pipeline design.

There are the following registers:

  • 32 general purpose 8-bit registers, r0-r31; with some alias like x=r27:r26, y=r29:28 and z=r31:r30
  • pc 16- or 22-bit program counter
  • sp 8- or 16-bit stack pointer
  • sreg 8-bit status register
  • rampx, rampy, rampz and eind

Usually r0 and r1 are fixed as usage.