Computers, and microcomputers in particular, are among the most useful tools that humans have developed. They are not the news media’s mysterious half-human forces implied by “The computer will decide . . .” or “It was a computer error!” No, computers are actually like levers; as a lever amplifies what the human arm can do, […]

Basic Computer Structure (Microcontrollers)

1.1 What is a microcomputer, and how does it execute the instructions that a programmer writes for it? This question is explored now at a level of abstraction that will be adequate for this text. We do know that many readers will object to one aspect of the following discussion, and we want to answer […]

The Instruction (Microcontrollers)

1.2 We now examine the notion of an instruction, which is an indivisible operation performed by the MPU. It can be described statically as a collection of bits stored in memory or as a line of a program or, dynamically, as a sequence of actions by the controller. In this discussion we begin with a […]

A Few Instructions and Some Simple Programs (Microcontrollers)

1.3 Now that we have examined the instruction from static and dynamic points of view, we will look at some simple programs. The machine code for these programs will be described explicitly so that you can try out these programs on a real 6812 and see how they work, or at least so that you […]

Variable Word Width (Microcontrollers)

1.5 We have glibly stated that a 6812 can have either 8-bit or 16-bit word widths. The fastidious reader might wonder how this takes place. This optional section provides details on how a 6812′s word widths can be either 8 bits or 16 bits wide, as discussed. The word width is a function of the […]

MC68HC812A4 and MC68HC912B32 Organizations (Microcontrollers)

1.4 The 6812 is currently available in two implementations, which are designated the MC68HC812A4 (abbreviated the ‘A4) and MC68HC912B32 (abbreviated the ‘B32). These are discussed herein. The ‘A4 can operate in the single-chip mode or the expanded bus mode. In the single-chip mode, the *A4 can be the only chip in a system, for it […]

Summary and Further Reading (Microcontrollers)

1.6 In this topic we examined the computer and the instruction in some detail. You should be prepared to study each of the instructions in the 6812 in the following two topics with respect to the details that we introduced for the load instruction in this topic. We will expand the ideas of programming, introduced […]

The Instruction Set (Microcontrollers)

In our study of how the computer ticks, we think that you will be motivated to read this topic because it will describe the actions the computer can do. It will supply a key ingredient that you need to write programs, so that the computer can magnify your ideas as a lever can magnify your […]

Move Instructions (Microcontrollers)

2.1 Behold the humble move instructions, for they labor to carry the data for the most elegant instructions. You might get excited when you find that this computer has a fairly fancy instruction like multiply, or you might be disappointed that it does not have floating-point instructions like the ones most big machines sport. Studies […]

Arithmetic Instructions (Microcontrollers)

2.2 The computer is often used to compute numerical data, as the name implies, or to keep topics or control machinery. These operations need arithmetic instructions, which we now study. However, you must recall that computers are designed and programs are written to enhance static or dynamic efficiency. Rather than have the four basic arithmetic […]