Instruction categories
This section presents the categories of instructions available in the 6502 processor. The purpose of discussing the 6502 here is to introduce the concepts associated with the instruction set of a processor architecture that is simpler than the modern 32- and 64-bit processors we will examine in later chapters. By the time we get to those processors, the underlying instruction set concepts should be quite familiar.
Memory load and store instructions
The 6502 uses load and store instructions to read data values from system memory into processor registers and to write registers out to system memory. In the 6502 architecture, the LDA, LDX, and LDY instructions load the register identified in the instruction mnemonic with an 8-bit word from system memory. LDA supports all addressing modes available in the 6502, while LDX and LDY each support a more limited subset of addressing modes: immediate, absolute, and absolute indexed.
After each of these instructions...
