Designing Embedded Hardware

Chapter 5. The PIC Microcontrollers

Where a calculator on the ENIAC is equipped with 18,000 vacuum tubes and weighs 30 tons, computers in the future may have only 1,000 vacuum tubes and perhaps weigh 1 1/2 tons.

—Popular Mechanics, March 1949

To start our exploration of microprocessor hardware, let’s look at the basics of creating computer hardware by designing a small computer based on a simple 8-pin PIC processor, the Microchip PIC12C508. The same design principles apply to the AVR and many other microcontrollers. This PIC processor is so simple that building a computer based upon it is trivial, as you will see. I’ll also take a look at a midrange PIC processor and show just what you need to do to design an embedded computer based on one. Before getting into designing computers, let’s take a quick tour of the PIC architecture.

A Tale of Two Processors

In the late 1970s, General Instruments had a 16-bit processor, known as the CP1600. It has long since passed into extinction and is all but forgotten, losing out to the Intel 8086 and the Motorola 68000. The trouble with the CP1600 was that it had limited I/O capability, and so General Instruments designed a tiny companion processor to act as an I/O controller. The idea was that this controller could provide not only the I/O for the CP1600, but also, being a processor in its own right, it could provide some degree of intelligent control. This processor was called the Peripheral Interface Controller, or PIC. The CP1600 died a quiet ...