Newbie question about first project.

Discussion in 'VHDL' started by Mike Deblis, Feb 6, 2004.

  1. Mike Deblis

    Mike Deblis Guest

    Hi,

    Be gentle, please! I've started reading "The Student's Guide to VHDL" and
    have puchased a CoolRunner II Development Kit from Xilinx (very nice and
    reasonably priced) - the kit gave me all the s/w I think I'll need for a
    while, though the manual is rubbish, hence the book. Book seems very good -
    accessible and easy to use - about half way through now - I program
    professionally anyway, and have an EE background, so its not too tough
    (quite fun actually...).

    Now, I know very little about this subject, but I like making clocks... Is a
    digital alarm clock (7 seg LEDs or other display technology) a reasonable
    project to start out with? Normally I'd have done this with a PIC or AVR,
    but it occurred to me that using a CPLD would be... well... different....

    But is it sensible? I would appreciate any comments on this approach,
    preferably helpful ;-)

    BTW. This is *not* a student project - my student days were about 25 years
    ago, hence my having "fun" learning different stuff...

    Many thanks

    Mike
     
    Mike Deblis, Feb 6, 2004
    #1
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  2. Mike Deblis wrote:
    >
    > Now, I know very little about this subject, but I like making clocks... Is a
    > digital alarm clock (7 seg LEDs or other display technology) a reasonable
    > project to start out with? Normally I'd have done this with a PIC or AVR,
    > but it occurred to me that using a CPLD would be... well... different....


    This is off-topic for this group, but I'll answer anyway, just this
    once. In future, implementation questions like these are better posted
    to comp.arch.fpga.

    As a VHDL project, this is a very reasonable first project. However,
    depending on the size of the CPLDs included in your dev. kit, this is
    either fairly easy, difficult, or impossible in a CPLD.

    CPLDs have a very limited number of flip-flops available (the number of
    FFs is given by the macrocell count). You will need at least 20 FFs for
    counters for the time. Assuming a 32768 Hz crystal for the clock, you
    will need 15 FFs to divide this down to 1 Hz. You will need at least 14
    FFs for the alarm register. Multiplexing a 7-segment display will
    require at least 17 FFs. That is a minimum of 66 FFs for a
    straightforward design. There are tricks you can use to reduce this
    number but they will only save a few FFs at the expense of significant
    complexity. This means you need to have at least an X2C256 or XCR3128XL
    available in your kit before you should even consider trying this. If
    you use 60 Hz as your clock (6 FFs instead of 14 for the divider), you
    MIGHT be able to squeeze it into a 64-macrocell device.
    --
    Tim Hubberstey, P.Eng. . . . . . Hardware/Software Consulting Engineer
    Marmot Engineering . . . . . . . VHDL, ASICs, FPGAs, embedded systems
    Vancouver, BC, Canada . . . . . . . . . . . http://www.marmot-eng.com
     
    Tim Hubberstey, Feb 6, 2004
    #2
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  3. Mike Deblis

    Mike Deblis Guest

    "Tim Hubberstey" <> wrote in message
    news:...
    > Mike Deblis wrote:
    > >
    > > Now, I know very little about this subject, but I like making clocks...

    Is a
    > > digital alarm clock (7 seg LEDs or other display technology) a

    reasonable
    > > project to start out with? Normally I'd have done this with a PIC or

    AVR,
    > > but it occurred to me that using a CPLD would be... well...

    different....
    >
    > This is off-topic for this group, but I'll answer anyway, just this
    > once. In future, implementation questions like these are better posted
    > to comp.arch.fpga.


    Sorry about that, I'll repost there...

    > As a VHDL project, this is a very reasonable first project. However,
    > depending on the size of the CPLDs included in your dev. kit, this is
    > either fairly easy, difficult, or impossible in a CPLD.

    [... snip ...]

    I think the kit uses an X2C256, so I may be OK there. I really appreciate
    your comments and I'll try in the correct group.

    Thanks again,

    Mike
     
    Mike Deblis, Feb 6, 2004
    #3
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