Note: It will help to have a HCS08 Microcontroller data book before following this article!
Let us start by considering a set of four HCS08 instructions. They are the main subset of the load/store instructions. Two involve register A and two the H:X pair as a main participant. The register-A instruction’s operand points to a single byte of memory to load from or store into. The register-H:X instruction’s operand points to a double byte of memory. The operands of all four look identical, we must tell from the opcode whether they will be reading that location or writing to it and whether it reads or writes one byte or two. We also must “know” from the architectural specifications of the computer (the details we need are in Table 7-2) that for the H:X instructions, the operand points to the memory location used with H and that the location used … Read More