Designing Embedded Hardware, 2nd Edition

Chapter 14. 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 ½ tons.

— Popular Mechanics, March 1949

This chapter introduces you to the Microchip PIC. To start our discussion of microprocessor hardware, we'll look at the basics of creating computer hardware by designing a small computer based on a simple 8-pin PIC processor. The same design principles apply to the AVR and many other microcontrollers. This PIC processor is so simple that building a computer based on one of them is trivial, as you will see. From there, we'll look at a mid-range PIC processor and see just what you need to do to design an embedded computer based on one. First, though, let's take a quick tour of the PIC architectures before getting into designing some computers.

A Tale of Two Processors

In the late 1970s, General Instruments had a 16-bit processor known as the CP1600. It has since passed into extinction and is all but forgotten, long ago losing out to the Intel 8086 and the Motorola 68000. One major failing of 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 being a processor in its own right, it could provide some degree of intelligent control. This processor was called the