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looking to place some sequential logic on to a programmable device!

Discussion in 'Electronic Design' started by Andrew Crook, Oct 22, 2003.

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  1. Andrew Crook

    Andrew Crook Guest

    I am looking to place some sequential logic on to a programmable device
    because I need to reduce the size of the circuit and one ic would be great.

    I know nothing about how to do this, but have been told I need to use a PLD.

    these look expensive and to complex for what I am doing

    I guess for this project I need the smallest cheapest available

    most of my circuits are based upon nand gates and d type latches, I may need
    to design something like a 555 for a buzzer.

    could somebody suggest one and a writer for it?

    many thanks for listening

    Andi
     
  2. Fred Bloggs

    Fred Bloggs Guest

    The cheapest will be the "In-Circuit Programmable" types with a homemade
    programming cable for the LPT port and using free software from the
    manu's- like Altera, Xilinx, Lattice, and Cypress. Many will sell the
    IC's online- something like $3-4 per copy. The downside is the minimal
    configuration will be something like 36 macrocells in a 44-PLCC, so you
    are looking at a pricey socket. The PLD are still available, but
    start-up costs are out of the question because they require specialized
    programmers executing proprietary algorithms and cost hundreds of dollars.
     
  3. Frank Buss

    Frank Buss Guest

    If it doesn't have to be too fast (say some 100 kHz), you can use a PIC.
    Take a look at the homepage of the producer for datasheets:

    http://www.microchip.com

    And try google for example for the 16f628, which is often used for small
    projects.
     
  4. Andrew Crook

    Andrew Crook Guest

    The PLD are still available, but
    i was looking at
    http://tutor.al-williams.com/pld-1.htm

    if I could draw my sequential logic circuits, mainly nand gates and d type
    flip-flops, in the software and write in to a cheap simple PLD (classic)
    that would be great. what do you think...

    any other ideas

    Andi
     
  5. Andrew Crook

    Andrew Crook Guest

    for about $3 for a PIC12F675-I/P ( i cant seem to find a data sheet) chip
    this is the best solution so far
    a compatable writer for $99.95.. any cheaper i would like to know!

    my only problem would be choosing the software as i have not used this setup
    before!
    i would like a simple cheap version basic to begin with, good support and
    documentation

    Andi
     
  6. Frank Buss

    Frank Buss Guest

    It is all on the Microchip-site, only some clicks from start:

    http://www.microchip.com/download/lit/pline/picmicro/families/12f6xx/41190c.pdf
    There are cheaper solutions, but for example with the PICSTART Plus
    you'll get the serial port pluggable writer and the software for
    programming, simulation on PC and writing nearly all PICs. It's worth,
    if you plan to do more with PICs in future.
     
  7. Frank Buss

    Frank Buss Guest

    Note: I don't get money for this recommendation and there are very good
    other microcontrollers from http://www.atmel.com/ and
    http://www.cypress.com/ , but I've tried PICs only and don't have any
    experience with other microcontrollers.
     
  8. Altera would be one option then. Their interface is graphical (as well as VHDL).
    The Base package, which is free, can do up to the MAX7000 series. However, Altera is pricer than
    most others.
    I have a schematic for their maxblaster LPT programmer, and have built my own.
    email me if you need the board files to construct your own.

    Cheers
     
  9. Paul Burke

    Paul Burke Guest


    My advice is DON'T do it that way. You know what you want- otherwise you
    won't be able to draw the circuit as gates and flipflops. Write out what
    you want as pseudocode, for example:

    when (A OR B) == 1 // Set condition
    Latch 1 = 1
    else when (A AND B) == 1
    Latch 1 = 0 // Reset condition
    else
    Latch 1 = Latch 1 // Hold condition

    Then get hold of a suitable software suite, I'd choose Lattice or Xilinx
    but that's on;ly because I've been using them for years. Rewrite using
    the appropriate syntax for the languages available (I find ABEL much
    easier than VHDL, others will differ). Compile and fit. If it won't fit
    in the smallest device, choose the next one up. If your logic is simple
    and small it will fit.

    Then buy the devices! Xilinx Coolrunner 64 logic block parts are only
    about £2.50 each in small quantities, and the amount of heartbreak they
    save is worth every penny. You can get them in PLCCs so prototyping is
    no bother. Lattice small ones (1016E, 2032 etc) are also quite cheap.

    Paul Burke
     
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