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Registered: ‎10-25-2017

Looking for competent person to implement an interface between 3v/5v devices (Pi/Apple2) on a CPLD (XC9500XL?) or FPGA


I've created a device that needs to interface a 3v Raspberry Pi with a 5v retro Apple II. I had this all done using transceivers and octal flip-flops as I'm using a single GPIO on the Pi side to send data serially and buffering them to form 8-bit values that can be read on the Apple II side, and vice-versa. The circuit contains all the logic necessary to do voltage translation and direction and control lines, etc...  while I use the Pi GPIO to signal when things should happen via control lines. The reads are solid (left it running overnight constantly reading RAM with zero errors) but the writes exhibit 5 errors out of every 10 million writes, which is due to the very small 25ns write window on the II bus and trying to use the Pi GPIO to control the timing. I'd like to replace this circuitry with a CPLD (or FPGA) and though I started learning some Verilog in order to achieve this I have a lot on my hands right now with family and kids in this Covid era that I figure I could freelance the work out to save me some time and give someone a bit of work. It's not a lot, but it's something.

The modern CPLDs do not have the 3.3/5v capabilities that the old XC9500XL does so I figure the XC9500XL might just be the right CPLD for the job, but it doesn't matter to me what CPLD (or even FPGA) is used so long as it does the job. The device is meant to sit on a peripheral board so the smaller the better.

Let me know if you're interested!


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