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'...
Over Christmas, I've been writing the software for the PS/2 interface, this will run on an stm8s003f3 from Mouser, they are an eyewatering £0.67 in the TSSOP package and £0.325 QFN but as I cannot solder QFN by hand it will by the TSSOP. They run at 16MHz which is faster than the base Z80 but the same as final Z80 version based on the Z84C1516FSG. The Z84C15 is a Z80 at 16 Mhz with the support chips of the KIO (SIO, PIO & CTC) it is still in production. The stm8 and the Z80 will communicate via the serial link at up to 460800 baud, the Z80 side will likely limit it to less than this. If I get around to an eZ80 version that will communicate using I²C freeing up the UART. The software I'm currently working will drive 2 ports one for keyboard and one for a mouse. The devices I'm using to test are USB via a PS/2 adapter, the genuine PS/2 parts seem to be a bit problematic, it may need a pull-up or pull-down resistor. The source can be found on GitHub in the STM8 subdi...
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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