Introducing Our Chip

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We are working on a project to build a simulator for a typical computer system. While we could invent such a machine from scratch. I feel it will be more useful to model our simulator after a real processor.

Looking around in my parts bin, I found an ideal candidate:


This little chip has some impressive features. You can buy one of these for as little as about $1.25, making it a nice part for experiments!

Here are the basic features of the chip:

  • Clock speed: 20MHz
  • Program Memory: 8KB Flash Memory (16 bit words)
  • Data Memory: 512 Bytes
  • 120 Instructions
  • Internal Timers, A/D converters
  • Six I/O pins (4 is using an external crystal to control speed)

We will look at the internal features in more detail later. FOr now, let’s take a quick look at the internal structure of this chip.


Don’t panic! This is just a Harvard Machine, and it works just like we have been discussing.


We will not go into detail about this processor now. We need a bit more background before we can really start work on simulating this chip.

Processor Data Sheet

In ancient times, manufacturers of electronic parts would publish a sheet of specifications for the part, so designers could build systems using those parts. For some reason, the term stuck. Today, we have a “data sheet” for a processor that could weight in at 500-100 pages in a PDF file!

Here is the “data sheet” for the AVR chip we will be modeling. We will examine the instruction set in this processor, but not much about its electrical properties: