Instruction encoding techniques for microcontroller architecture

Abstract

Code and instruction encoding extensions to a microcontroller architecture provide backward compatibility with an existing microcontroller while allowing significant performance enhancements as a result to the new architecture. An extension to provide additional instruction codes has been implemented while retaining backwards compatibility so that the instructions for the prior processor retain their functionality by utilizing one unused opcode in the prior processor's opcode map. In this connection, two modes of operation are provided, namely binary and source modes. The entire instruction set is available in both modes, but the encoding is different. In the binary mode, all of the instructions of the prior processor keep their encoding. The additional instructions have an ASH prefix, ASH being the single unused opcode. In source mode, some of the instructions from the prior processor known as register instructions have the AS prefix, thereby freeing up 160 opcodes for more important instructions. Since the register-based instructions of the new processor provide better performance than the instructions that they replace, there is no need to use the old register based instructions. Therefore, adding a byte and a state to the old register instructions results in a negligible penalty. In source mode, the instructions for the new processor do not require the AS prefix. This shortens these instructions by 1 byte in length and speeds up the execution by 1 state.