Instruction Set and Class

Summary

This chapter focuses on perhaps the most important characteristic of an ISA (Instruction Set Architecture), which is a processor's instruction set. It defines and proposes how to classify instructions, and then present the different instruction families for a generic microprocessor as well as the possible extensions for this set. The process of classifying instructions generally relies on the locality of execution or processing. Instructions can be classified into three main families or classes, one for data transfers, one for arithmetic processing instructions for integers and logical instructions and one for control transfers. One of the three MPU (Micro Processor Unit) functions, aside from their processing and storage, is data transfer. The chapter illustrates the execution path is divided by the branching instruction (or node) into two paths, the fall‐through path and the target path. If the condition is true, then the control transfer is made at the instruction on the branch target address.