7.4.5 Register File

The register file consists of 32 8-bit general purpose working registers used by the CPU. The register file is located in a separate address space from the data memory.

All CPU instructions that operate on working registers have direct and single-cycle access to the register file. Some limitations apply to which working registers can be accessed by an instruction, like the constant arithmetic and logic instructions SBCI, SUBI, CPI, ANDI, ORI and LDI. These instructions apply to the second half of the working registers in the register file, R16 to R31. See the AVR Instruction Set Manual for further details.