Fadal Archaeology: 1400-2 CPU Card

I’ve been spending more time lately diving into reverse engineering of the Fadal CNC control. I upgraded my CPU card to a 1400-2 so that my control would have look-ahead and continuous contouring. This feature was lacking in the 1400-1 CPU and caused the machine to pause briefly between linking moves.

After acquiring the 1400-2 CPU I tried using my 1460-0 memory expansion with it, and while I got it working, according to the Fadal board compatibility matrix, this is not a supported configuration. I went on eBay and looked for the 1460-1 memory expansion and was underwhelmed how simplified and cost reduced it was in comparison to the 1460-0. This reignited an idea I had during my last reverse engineering sprint: why not design and build my own memory expansion? Well, after a bit of reverse engineering and a couple board revisions and component revisions, I got a working result. I now have a single board 384KB solution just like the 1460-2 board for the later controls.

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Fadal 1400-1 CPU Card Reverse Engineering and Schematic

This article originally appeared in My little (home) shop thread on Practical Machinist.

I only worked on the CPU board schematic a few minutes today, but I finished all the address decoding logic.

The 8088 only has 20 address lines, of that, 16 of them are used for addressing segments of 64KB each. The address lines A16 through A19 are used as card selects to talk to the peripheral cards. There is a 4 to 16 line decoder that takes the upper nibble of the CPU address, then converts that to a selector that is 1 of 16 lines on the bus. Fadal repurposed a bunch of address and logic lines to make these card selects.

A 20bit address is represented as 5 hex nibbles, like 0xFBC00, that’s segment 15, address BC00. That happens to correspond to the video memory on the video card. The first F selects card 15, which is the video card (we are talking base 0 numbers here, so 0-15), the BC00 selects the base address within the F segment. The F segment also contains the system ROM, which is located at FE000-FFFFF, an 8KB chunk. The video ram is only 1KB, so it occupies addresses FBC00-FBFFF.

It would seem that the memory expansion cards occupy a card select range, though I’m not certain exactly where the memory and NC executive ROMs are mapped yet. Once I have the schematic completed and the system ROM reverse engineered, I could design my own memory expansion card.

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Fadal 1420-1 Video Card Reverse Engineering and Schematic

This article originally appeared in My little (home) shop thread on Practical Machinist.

I finished my reverse engineered schematic of the Fadal 1420-1 video board. I’d estimate I have 20-25 hours into the schematic at this point.

The schematic, and observation of the control display, lead to some interesting observations about the original design.

It’s widely told that Adrian de Caussin is the one who designed the control hardware, unfortunately he passed away some time ago (a reference from 1996 indicates he’d passed by then), so this public accounting may be the only hardware level details known outside of the de Caussin family.

I did reach out to David de Caussin the younger to try and learn details about the original control development, because at this point they are considered vintage computer systems. Unfortunately I didn’t receive a reply from him, so I had to go at it myself.

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Fadal Chargen ROM Reverse Engineering

This article originally appeared in My little (home) shop thread on Practical Machinist.

Fadal Chargen ROM

That’s the contents of the character generator ROM on the Fadal video card. I used a Parallax Propeller development board to make a breadboard EPROM reader.

I’m interested in making a video card that will plug in place of the Fadal card and output a video format of my choosing.

Specifically I’m talking about using a Parallax Propeller microcontroller to generate a VGA signal. The picture is actually the Propeller outputting the ROM data to a VGA monitor.

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Fadal CNC Reverse Engineering

This article originally appeared in My little (home) shop thread on Practical Machinist.

Just to be clear, the control and electronics work fine on my Fadal at present, it was the iron that needed major help.

The process of reverse engineering the control started with researching the history of the Fadal control. On the VMC Electric website they give a few pieces of information about the process of creating the control.

They said they used an Imsai 8080 to develop the NC executive. If you read closely you’ll see they used the NC software to process G-code into NC tapes for their other machines. This specifically includes applying cutter radius compensation and other stuff that old NC systems couldn’t do.

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