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Low cost and/or small size CPU in an FPGA

Discussion in 'Electronic Design' started by hamilton, Apr 24, 2013.

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  1. hamilton

    hamilton Guest

    The discussion has got me to wonder, what is the lowest cost and/or the
    smallest CPU in an FPGA.

    Can a CPU with reasonable code space fit into a 44 pin FPGA ?

    Are there any 44 pin FPGAs ?

  2. Uwe Hercksen

    Uwe Hercksen Guest


    if we only look for the needed pins, these CPUs would fit:
    separate 8 bit data and 16 bit address bus
    separate 16 bit data and 16 bit address bus
    separate 16 bit data and 20 bit address bus
    multiplexed 16 bit data and address bus
    multiplexed 16 bit data and 32 bit address bus
    multiplexed 32 bit data and address bus

    The number of gates necessary depends on the size of the instruction
    set. A RISC CPU with serial processing in the ALU would be slow but small.

  3. Guest

    I think limiting factor is usually memory, not the cpu

    guess you could do something with an external serial flash
    some of them a quite fast, and it wouldn't take much logic
    to take advantage of the read address auto increment

  4. hamilton

    hamilton Guest

    Ok, my goal.

    I need a uP and some logic, but I would like to do it with one part.

    208 pins just won't fit into my package.


  5. Nico Coesel

    Nico Coesel Guest

    I've used the Picoblaze CPU from Xilinx in several projects. AFAIK
    that is the smallest useful FPGA cpu.
  6. rickman

    rickman Guest

    Have you looked at any of the FPGA lines yet? If package is a big deal,
    you need to pull up some data sheets and check out the packages.

    The parts I have used or will be using are the XP from Lattice in the
    100 pin QFP and the iCE40 also from Lattice in several useful packages.
    The iCE40 data sheet shows a 32 pin QFN, an 84 pin QFN and 100 and 144
    pin QFP. Everything else is some fine pitch BGA which I prefer not to
    use because of the small drills and fine pitch required of the PCBs.

    Xilinx and Altera may have some parts in non-BGA packages too, I'm not
    so familiar with those lines. Both of the Lattice families I mention
    have on chip Flash or one time programmable memory. That saves a chip
    or two for programming.
  7. rickman

    rickman Guest

    BTW, you might want to post this to comp.lang.forth They discuss MISC
    often there.
  8. ADUC702x has a quite simple programmable array (just combinatorial
  9. hamilton

    hamilton Guest

    I want to thank everyone that made suggestions.

    I have discovered the SAM4S 120Mhz processor in a 48-pin package.

    The I/O pins may be able to do in software what I wanted the logic to do
    on a slower processor.

    I can create a 100nSec pulse in software.

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