Bah Humbug


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Ace

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A few months ago I found I had enough time on my hands to get on with something I 've been planning for 20+ years and that was to create a new Jupiter Ace. At one point I'd started porting the ROM to the Raspberry PI bits of it even run, but the problem was that the PI is quite a closed system finding out the details of the CPU and Graphics system is difficult and hidden behind a veil of secrecy and IP. The system I wanted to create would be simple and easy to understand at all levels. The first step was to find some schematics in a system I could get for free. Bodo Wenzel had done some nice ones here but in OrCAD which costs money. He did, however, provide images of the work so off I set with the free version of Eagle CAD. I downloaded the PDFs to get a good look. I translated the above eventually to Which is available in KiCad format here . Then built a cut down version to show the diagrams were correct. All the routing is done by FreeRouting because I'...
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DiagBoard

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To help me develop DEUCE, I created a simple diagnostic board, which includes a single step, reset, and LEDs for all the pins on the edge connector. It also has some duplicate pins, so I can easily use a Logic Analyser plus some power pins to allow connections to other stuff.  The ICs, on the right, are hex buffers to minimise interference with the main board. Only the RESET and WAIT lines can change the signal at the CPU.    This is a video of me powering it up in single-step mode, then doing some steps, letting it run for a while, and then back to single-step. While it is in step mode, the screen misbehaves. This happens because the software is accessing the Video RAM and locking out the VDG. The software is my little test harness which can be found on GitHub here .  The design for the diag board is also on GitHub here . There are some slight differences from this version. One is changing a label on a pin, and the other is adding a PWR LED.
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Interrupted

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It has been a while. Full-time paid employment means I have enough cash to finish this but limits the time I can spend finishing it. The current state of play it that I have added some SMDs to get in some practice with those. One of the SMDs is a frequency multiplier so that with the original crystal to drive the video I can vary the CPU speed from the 3.278MHz of the original ACE up to 19.668MHz and perhaps beyond. I've also made some modifications to make the KIO optional and enable full ACE compatibility. The KIOs are very difficult to get hold of and with Z84C15 and Z182 available these seem like the best CPU to be going forward. The fastest CPU I have is 20MHz and while I had to up the speed of the RAM, everything else seem happy on the CPU side. The Video was less happy, but I am not 100% convinced that was a speed problem. The multiplier I'm using on this board is a Renesas 512MLF , which is pin compatible with the On Semiconductor NB3N502DR2G , though the multiplicat...
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