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 Forum index » DIY Hardware and Software » Microcontrollers and Programmable Logic
Newbie to Xilinx FPGA programming asks.......
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mubase



Joined: Mar 24, 2011
Posts: 110
Location: London UK
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PostPosted: Tue Jan 29, 2013 11:40 am    Post subject: Newbie to Xilinx FPGA programming asks.......
Subject description: 76477?
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Hi. I am a newbie to FPGAs but am very interested in learning to use them. I have got a Papilio one 500K and a logicstart board from gadgetfactory.http://www.gadgetfactory.net/

I knwo some boolean and digital logic having studied the rudimentaries in College ( an audio electronics class, bizarrely.) so I know my nands from my exors, what de-morgans is and I could probably do karnaugh if I refreshed myself.
I have a question regarding FPGA. I know I am nowhere near any kind of level to be able to acomplish this but...


Would it be possible to synthesize a 76477 on an FPGA board?

I have seen some great sites about what FPGAs can do audio and synthesis wise.. very very cool.
But a 76477??

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JovianPyx



Joined: Nov 20, 2007
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PostPosted: Tue Jan 29, 2013 2:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi and Welcome to insanity.

I've just looked around and can't find a true internal schematic for the 76477. It looks like it is not pure digital though, from the block diagram. As you may know an FPGA is a collection of digital logic blocks and there is no analog "stuff" in it. The block diagram may be sufficient to put together bits of DSP logic to achieve the same or similar results. Note however, that an FPGA by itself will not accept an analog voltage (like a control voltage) without the use of an ADC, so some additional circuitry would be needed to make the FPGA compatible with some (unknown) schematic that uses a 76477. There's really nothing special (in my opinion) about the 76477 or it's sound. Arcade game sounds basically. This kind of thing should be possible to model using an FPGA.

However, with that said, I think there is so much more that you can do with an FPGA of 500K equivalent gates. In fact, a rather complex high fidelity 8 (or more) voice polysynth is possible. Things that suck about the 76477 IMO are the noise generator. An FPGA will allow you to do far far better with something like a 32 bit or 64 bit LFSR as opposed to the very short LFSR that is in the 76477 that you can hear repeat if you clock it fast - you'd have to wait for years to hear a repeat with a 64 bit LFSR.

So generally, the answer is "yes", you should be able to make DSP logic in an FPGA sound like a 76477 (assuming you have the addtional hardware such as DAC and ADC).

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yogi



Joined: Jun 26, 2008
Posts: 26
Location: Maryland

PostPosted: Thu Feb 07, 2013 3:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi, MuBase. Another Papilio owner! I too have a 500K but I haven't been to active with it yet. You may know of Gadget Factory's RetroCade, though it's targeted towards the new Papilo Pro, Jack has mentioned that he may release a '500K' simplified version (may be done already). Also there are both the SID and YM 2149 IPs as well as ScottG's Gateman Poly synth and Stefan's SK-synth 'ported' to the Papilio hardware (kind of hard to find on the GF sites, in the sandbox area I think).
The RetroCade mega wing adds allot to the party, with Midi connectors, audio jacks, LCD, joystick and micro SD card. Unlike the Dev boards the megawing doesn't include a codex but relies on the ZPUino softcore and Delta Sigma DAC IP.
Like I said, you probably already know about all the above, but if not...just say'in.
DISCLAIMER- Don't have anything to do with Gadget Factory, just excited about FPGA synthy stuff (got mine after seeing the great designs @ FPGA-Synth wiki, Thanks JovianPyx! 'Laughing').
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