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In her latest Intersil “Academy of Analog Pinball Wizardry” video, Jeri Ellsworth replaces an HC55564 Continuous Variable Slope Delta (CVSD) codec chip with one she reversed engineered into an FPGA. What in blue-blazes is a CVSD modulator? Watch the vid and find out — as usual, Jeri does a great job of showing how it works, how she reversed engineered it, and what the results are. As some have pointed out, you can still scare these chips up online, but this was more about proving and showing than just about fixing.

Continuous Variable Slope Delta Modulator – HC55564

Gareth Branwyn

Gareth Branwyn is a freelancer writer and the former Editorial Director of Maker Media. He is the author or editor of a dozen books on technology, DIY, and geek culture, including the first book about the web (Mosaic Quick Tour) and the Absolute Beginner’s Guide to Building Robots. He is currently working on a best-of collection of his writing, called Borg Like Me.



  1. John Mangan says:

    Wow, amazing job Jeri! (as always). I would love to see more of the actual process that you use to get this information.

    1. Anonymous says:

      Good point, John. I had the same thought, watching the vid. I understand enough to know, conceptually, how this sort of thing works, but I have no idea how you actually go about getting the information on how the chip functions out of the chip itself(?). I assume all of this was not from data sheets and info found online. I’ll try and get Jeri over here to give us some clues.

  2. Anonymous says:

    Grammar police: “… and what the result is” (not are).  Or “results are”, take your pick.

    Otherwise excellent!

    1. Anonymous says:

      Oops. Yes. Typo. Missed the “s.” Fixed.