Microprocessor systems and microcontrollers

Microprocessors play an important part in modern day life. They are used to control domestic appliances, like the microwave cooker, car engine management and braking systems, cash dispensing machines, mobile telephones and so on.

In most applications, the microprocessor takes in information from the outside world, processes it in some way and uses the result to control some device, such as a motor, or heater, or displays the outcome on a monitor screen.

It is a programmable device, meaning that its behaviour is dictated by a list of instructions, called a program.

The microcontroller is a programmable device which can provide all the elements of a microprocessor system.

• processing
• memory, used to store the program which the microprocessor must follow, and data needed by or produced by the program,
• an input/output port, through which data is received from and returned to the outside world,
• and a clock, used to synchronise and regulate the flow of data around the system

Programming Language
The microprocessor receives its instructions from a program stored in memory. These instructions are in form of binary numbers, the only ‘language’ that the microprocessor, a digital system, ‘understands’. This is known as machine code.

Humans do not find it easy or efficient to use binary numbers, and so hexadecimal numbering is usually used to enter, or to list the machine code program.

High level languages e.g. BASIC, have been developed to make programming easier and bear a resemblance to everyday English.

An elaborate program called a compiler carries out the process of translating the high-level language into machine code. This process slows down the running of the program. Machine code programming is the most efficient in terms of memory space and execution time.

The complete list of instructions, which a particular microprocessor can execute, is called the instruction set. Each instruction can be described by a mnemonic, to make it intelligible to us, or as a hexadecimal or binary number. For example, ‘incf’ stands for ‘increment file’ meaning ‘add one to the number stored in the file (or register) referred to. The machine code for this instruction is the binary number 00 1010.

A program, then, is a series of numbers, identifying what instructions the microprocessor must carry out, together with any data it needs to do this. Embedded in the microprocessor itself, is a program containing the sequence of operations needed to execute each instruction.

The PIC program can be saved in two forms, either in machine code or in assembler language, (the mnemonics). The former is called the object file and the latter the source file.