GE PLC + Stellaris Launchpad

Updated CPU module for a GE Fanuc Series One PLC

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I had a lot of GE PLC parts laying around but no decent CPU to control them. I decided to build a new CPU module. I chose the TI Stellaris Launchpad since I already had one. The original CPU was an 8051 running at 2MHz with 4kB of program memory. The new one will have 256kB or program memory plus 16kB of ram.

The PLC uses a 9V data bus. I'm assuming this is to provide noise immunity. This was a problem since not many components can tolerate this voltage. Luckily the parts used in the old CPU are still made. The old CPU used a CD4504b and LS145 to interface between the high and low voltages.

Important things to know if you want to do it yourself:
1) All pins are active low except when writing data to outputs
2) Inputs are active low and have a settling time of about 125nS
3)The run relay needs to be pulled down with about 125mA draw

The board layout was done in Pad2pad.  The software was pretty self explanatory.  The boards turned out great.  I just wish I could have made them myself since they were a little expensive.  

The project uses an Ethernet transceiver for external connectivity.  This way it can be easily interfaced with other control software like LinuxCNC.  In the most basic mode it can be used as a field IO adapter without running any machine control code on the TI processor.  

  • 1 × Stellaris Launchpad
  • 1 × ENC28J60 Ethernet driver

  • Modbus is working!

    Ben Kopietz09/30/2014 at 01:43 0 comments

    I got the Modbus TCP server working.  It was tested using Fenix Modbus. 

    The completed code is on git hub as a separate project.  

  • Project Report

    Ben Kopietz08/10/2014 at 22:37 0 comments

    I added a detailed report about the development into the Github files.  That goes through the whole development process. 

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PointyOintment wrote 08/08/2014 at 16:55 point
Can it still be programmed with ladder logic?

  Are you sure? yes | no

Ben Kopietz wrote 08/09/2014 at 01:45 point
It can't. I have been using Code composer studio in C. I was pondering making a ladder logic program that would output C code that I could compile and download.

  Are you sure? yes | no

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