Processor Elements

This chapter begins our development of a comprehensive understanding of modern processor architectures. Building upon the basic digital circuits introduced in Chapter 2, Digital Logic, we discuss the functional units of a simple, generic computer processor. Concepts related to the instruction set and register set are introduced, followed by a discussion of the steps involved in instruction loading, decoding, execution, and sequencing. Addressing modes and instruction categories are discussed in the context of the 6502 processor architecture. We choose to focus on this venerable processor for its structural cleanliness and simplicity, which allows us to consider basic concepts without distractions. The requirement for processor interrupt handling is introduced, using the example of 6502 interrupt processing. The standard approaches that modern processors employ for input/output (I/O) operations are introduced, including direct memory access (DMA).

After completing...