Introduction

The purpose of this page is to develop a small controller that works like a PLC (Programmable Logic Controller). This page is for the people who want to use and work with PLC’s, maybe for home automation or just controlling your irrigation system, but who can’t afford to buy one of the commercial products. This project is part of a commercial project so I will make available as much as I am allow to. 

Features

I/O

I will test the program with the STK500 development System for now and later put some suggested hard together that will work. The hardware is not a fixed design, you would be able to adapt it for your application. Some people prefer open-drain outputs where other might prefer relay outputs, it doesn't matter. 

Software

The PLC will support the following Commands:

1. SOR - Start of Rung

2. EOF - End of Rung

3. BST - Branch Started

4. NXB - Next Branch

5. BND - Branch Ended

6. END - End of Logic

7. XIC - Examine If Close

8. XIO - Examine If Open

9. OTE - Output Energize

10. OTL - Output Latch

11. OTU - Output Unlatch

12. TON - Timer On

13. CTU - Count Up

14. CTD - Count Down

With these instructions you can create a very useful control system.

Enhanced PLC

I will also developed an enhance version of the PLC with integer math instructions, some analog I/O, and a real-time clock. Unfortunately this will not be available for free. This controller will be sold in a kit form. Due the mid of September, 2002.