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  1. #1
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    sequential and combinational

    Hi
    I have a few questions could you please explain them:

    1) the difference between combinational and sequential architecture.
    2)What happenes to speed when temprature of a cmos transistor increases.
    3)what is the difference between a flipflop and latch.
    4)what is the difference between a risc and sisc processor.
    5) what is the reason one chooses for state machines.

    Thanks

    •   Alt27th May 2004, 19:44

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    is latch combinational or sequential

    Ok, let's go one by one.

    1) the difference between combinational and sequential architecture.
    RE: A combinational circuit's output depends only on its current inputs. This means, it has a truth table. A sequential circuit's output depends on its previous inputs. This means, it's output will depend on which state it is.

    2)What happenes to speed when temprature of a cmos transistor
    increases.
    RE: Sorry, don't know

    3)what is the difference between a flipflop and latch.
    RE: A FF is activated by border and a Latch is activated by level. This means, the FF output will be the input that was present at the time we had the clock border(up or down). If the input changes right after the clock border, its output won't change. When it comes to latch, its output changes accordingly to the input while we have a level of voltage(the border means nothing to the latch).

    4)what is the difference between a risc and sisc processor.
    RE: It's the number of instructions recognized by the processor. RISC stands for Reduced Instruction Set Computer. CISC, stands for Complex Instruction Set Computer. Some say RISC computer tends to be faster and cheaper, since they have a small number of instruction. At the bottom, this saves transistors, but since it has a small set of instructions, it needs higher software work.

    5) what is the reason one chooses for state machines.
    RE: Instead of what ? Micro-controllers ? I think it is becouse you can make very low power circuits using state machines instead of microcontrolers. You can project your circuit to your needs so you don't waste power in functions you will never use like in the case of the micro- controllers.

    I hope my answers helpd you.
    mcoster



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    sequential and combinational

    Hi Mcoster
    Thanks a lot your answers did help me a lot
    Thanks



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    run fast stay cool transistor

    answers to all questions except 4 can be found in john wakerly's book digital design princples and practices. use the search function in edaboard.



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    diff between combinational and sequential

    btw: this post is relevant to the elect' beginners forum.
    do not affend.



    •   Alt29th May 2004, 10:50

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    difference b/w combinational & sequential circuit

    Quote Originally Posted by hawk
    btw: this post is relevant to the elect' beginners forum.
    do not affend.
    I have been only thinking that one architecture having feedback paths will be Sequencial Architecture. In other hand , a architecture not having any feedbacks path will be considered to be a Combinational Architecture.



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    differences between combinational and sequential

    Hi
    Regarding question 2, as temperature increases the Speed of CMOS Devices decreases, you have to worry about the mobility of the holes and the electrons, refer to Kang (CMOS) thats the reason why they say that if you can keep your computer cbinet cool you can make the processing faster..

    The other questions are more or less answered correctly by mcoster

    I thing I would like to add regarding the CISC vs RISC, is that in RISC there i tremendous saving in terms of the Die size, this is why you can find Loads of registers and other advanced features incorporated in the RISC Controllers.



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    latch sequential or combinational

    Another reason (even more significant) that higher temperature makes circuits slower is that higher temprature makes interconection wires more resistive.



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    the primary difference between sequential

    Two points:

    1) While it may be true that increased temperature will marginally degrade the performance of the (metal) interconnect, the first order effect will be on the transistors.

    2) Cooling your computer will not make it run faster. A cool cabinet may allow you to overclock your processor/memory to a higher speed, but just cooling the cabinet alone will not make it run faster.

    Radix



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    differences between sequential

    higer temperature will exacerbate the irregular heat movement of free electrons in the silicon, thus make more impedance to the current flow of these free electrons. Since delay time is propotional to R*C, R is bigger -> more delay time. That's why in worst case (higher temperature) the circuit is more likely to fail the setup time.



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    diff b/w sequential and combinational circuits

    I'd like to try to answer question 1 & 2 - basically I agree with the answers given in the reply posts.

    (1) Difference between combinational & sequential architecture? The existence of a memory element (latches or flip-flops in the circuit)! Memory elements defines a sequential architecture.

    (2) Relation between speed and cmos temperature? Well, personally, if you're talking about the speed of a computer or an electronics circuits, I don't think you should make any relations between the two. The dependency of a cmos transistor to temperature mostly affects the mobility of the electrons (or holes, if you prefer) in the transistor. Whereas speed - well, you usually define speed for a circuit by measuring how fast can a device/circuit can charge/discharge a given load. So, what I'm saying is although there is a very small relation between them, speed is actually more dependent on other external factors compared to the temperature of cmos transistors.

    If I'm wrong, my bad :p

    -lordwolf-



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