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Microcontroller or Memory

Discussion in 'Electronic Basics' started by Wong, Sep 4, 2003.

  1. Wong

    Wong Guest

    Hi,
    One of my friend told me that this is a microcontroller,

    Device type: EPROM/UV EPROM
    Company: ST
    Part number: M27C801
    Datasheet at: http://us.st.com/stonline/books/pdf/docs/4377.pdf

    Although I clarified to him that it is just a memory device, but he
    is still insist that it should be a microcontroller.
    Please tell me and my friend about the truth, any help will be
    appreciated.


    Best regards,
    confusing people
     
  2. Dana Raymond

    Dana Raymond Guest

    Uhhh, I don't think so. You need a latch to store the current state so that
    it will be presented in a stable way to the ROM to transition correctly to
    the next state. That also implies the need for a clock of some sort.

    Dana Frank Raymond
     
  3. Dana Raymond

    Dana Raymond Guest

    I'm sorry you are confused by this NG.
    When asking the question "Is an EPROM a MICROCONTROLLER" the answer is NO,
    and there is no room for confusion. A EPROM can form a part of a
    microcontroller but not a whole one, by any definition.

    The state machine that others have mentioned can be made from any type of
    ROM, but at least two other elements (a latch/FF and a clock) are required.
    In fact, the roles that an EPROM plays in a microcontroller, microprocessor,
    or state machine circuit are synonymous - it holds the programmed pattern of
    behavior, also known as the algorithms. But, no one would ever point to an
    EPROM in any of these circuits and say "That's the
    microcontoller/processor".

    In fact, microcontrollers and processors contain many state machines, the
    most complicated one, called the microcode execution unit, uses a ROM.
    Again, no one ever points to it and calls that ROM a microcontroller.

    The following site I found is interesting as it shows in a very clear way
    the three elements of a state machine.
    The ROM Memory map has as its address inputs the input terms A and B and the
    output from the state register. The state register latches the ROM output
    (state) and feeds that back to the ROM. A button on the page allows you to
    generate a clock pulse to 'step' the state machine.

    http://www.eng.dmu.ac.uk/~dinu/FSM.html

    I hope this serves to put this beast to bed.
    Dana Frank Raymond
     
  4.  
  5. ---------------------------
    State machines are built with clocks and latches merely to make them
    dead-easy to program. Otherwise countless race and ambiguous conditions
    have to be avoided and it takes more memory and many more steps. Also,
    they have to be naturally clocked by their states, which doubles or
    triples their size, and their vulnerability to the former problematic
    conditions. It can indeed be done, but it is more difficult. A little
    thought will enable you to make a simple one yourself, and to explore
    the increase in size even a simple addition would require.

    I helped write one once that with two eproms could speak my voice
    out of binary storage on one, and would speak the two digit temperature
    as fed it by an ADC and thermistor circuit, which answered and spoke
    repeatedly when called on the telephone. But that was 15 years ago.
    I'd have to hunt it up, and then I wouldn't publish it, it may STILL
    be patentable.
    -Steve
     
  6. Wong

    Wong Guest

    Hi,
    Dana sounds more reasonable to me. By any definition,
    microcontroller is formed by a processor and memory. It's hard for me
    to accept that you can get a *stand-alone* EPROM and make it a
    processor. If so, can you tell me how fast is your processor/EPROM
    without a clock, Steve? I am interesting too if Steve able to show us.
     
  7. ------------
    So, you have NEVER seen a speed rating on an EPROM or SRAM??
    Think about it...

    Of course the speed it will run on its own depends on the way it's
    programmed.

    -Steve
     
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