microcontrollers lab EGCP

Lab Objectives

The objective is to review the programmer’s model, the Motorola assembly language, and the instruction execution cycle. To achieve these objectives, you will write a short program(s) satisfying the requirements below.

Description

Programmer’s Model

The programmer’s model of the HCS12 shows the current status of the MCU. As the name implies, what is described is a model of the MCU rather than a physical entity. Although the model components physically exist in the MCU, they are only a small part of a complex implementation necessary for the working controller.

Motorola Assembly Language

The symbolic language used to code source programs to be processed by the assembler is called assembly language. The language is a collection of mnemonic symbols representing operations (i.e., machine instruction mnemonics or directives to the assembler), symbolic names, operators, and special symbols. The assembly language provides mnemonic operation codes for all machine instructions in the instruction set.

Instruction Execution Cycle

The instruction execution cycle is the sequence of actions taken by the HCS12 to execute a set of instructions. There three steps involved in completing each instruction: fetch, decode, and execute. During the fetch stage, op-codes and operands are loaded from memory to the instruction register. The decode stage interprets each instruction as one predefined CPU action. For many instructions, this decode stage overlaps with the fetch stage: as soon as the op-code is fetched from the memory, it is decoded. Once the necessary op-code and operand are loaded into the instruction register, the MCU moves into the execution stage. During this stage, the decoded instruction is executed.