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| Can't seem to find the right dev board for the job http://forum.6502.org/viewtopic.php?f=10&t=2993 |
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| Author: | Johnny Starr [ Wed Jun 25, 2014 5:03 pm ] |
| Post subject: | Can't seem to find the right dev board for the job |
A few months back, I was inspired by the BMOW project: http://www.bigmessowires.com/category/bmow1/ I know a lot of folks have made these TTL CPUs, and it seemed like a fun, long term project. I've learned quite a bit about digital logic and feel ready to start playing with actual hardware. I've thought about ordering a buttload of discrete logic ICs and either wirewrapping or breadboarding. Sadly, I don't have as much time for assembly as I would like. Right now, I don't have much of a workspace, nor do I want to keep up with dozens of wires and ICs. I'm a software engineer by trade, and I'm much more comfortable with work I can do at my work station. I discovered FPGAs and CPLDs not long ago and love the concepts. Verilog and VHDL don't scare me as I've worked with concurrent dev before. I think if I went the CPLD route, I would make the most of my time and money. Unfortunately, I'm having a really hard time finding the right dev board. I've found the DE-0 Nano which looks great, but seems like it might be overkill with 22,320 LEs. Some of the low-end CPLDs I've found are cheaper, but not that much cheaper. The really tiny ones are about $10 - $20 but lack programmers and don't have sufficient gates. I'm hoping to find a no frills board that will give me something to get started with that's easy to use. I'm hoping to implement an 8-bit CPU, so it will need enough gates to support that. Maybe I just need to spend the $80 and move on. I'm hoping for some feedback as it seems that you guys know a lot about these things. Thanks. |
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| Author: | BigEd [ Wed Jun 25, 2014 9:45 pm ] |
| Post subject: | Re: Can't seem to find the right dev board for the job |
I think previous discussions have concluded that CPLDs are too small for a 6502-like machine, although they are big enough for something minimal. The nice thing about programmable logic is that the tools are free and include a simulator. You can do most of your design work before you commit to specific parts, and once you have something of a design together you can see which parts will be big enough to hold it. My guess is that the smallest FPGA will be fine but the largest reasonably priced CPLD will be too small. As for a programmer, I think Xilinx-compatible programmers are a bit more expensive than others. For example this Altera board includes a programmer, for $30 all-in: http://www.ebay.com/itm/EP2C5T144-FPGA- ... 0961273878 Cheers Ed Edit: we have a thread on FPGA dev boards. |
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| Author: | GARTHWILSON [ Wed Jun 25, 2014 10:12 pm ] |
| Post subject: | Re: Can't seem to find the right dev board for the job |
Johnny, you may have seen his processor-in-a-CPLD project, at http://www.bigmessowires.com/cpu-in-a-cpld/. It has a subset of the 6502 instruction set and is very minimal. |
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| Author: | Tor [ Thu Jun 26, 2014 8:38 am ] |
| Post subject: | Re: Can't seem to find the right dev board for the job |
The DE0-Nano is a Cyclone IV FPGA development board. It's pretty powerful, a great board but not the cheapest one and possibly overkill. The sub-$30 board that Ed linked to (there are others out there too, I think I got mine for $17, but then again I already have a $6 programmer from before) is used in Grant's project here: http://searle.hostei.com/grant/Multicomp/index.html (Grant is a member of this forum) -Tor |
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| Author: | BigEd [ Thu Jun 26, 2014 9:15 am ] |
| Post subject: | Re: Can't seem to find the right dev board for the job |
(Thanks Tor - I'm sure Grant's project is the reason why I bought mine!) I feel I should add that if you're building a project out of multiple CPLDs then of course there's no limit to what you can make. Perhaps an obvious point, but I wouldn't want to dismiss CPLDs out of hand for the CPU designer. Garth, thanks for linking to Steve's TinyCPU - I had that in mind but didn't look up the link. It's notable that when he started he needed to use a pair of CPLDs, but more recent technology (but at 3V rather than 5V) allows him to fit everything into one big CPLD. |
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