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Thread: Signal generation

  1. #1

    Post Signal generation

    Hi,
    can someone explain to me, how +5V or 0V (binary) signals are generated and transported inside the system? What device generates and puts signals on the frequency generated by the system clock? Primarily a processor? Does the frequency strobe carrying a +5V (binary 1) signal look different to the strobe carrying 0V (binary 0) signal? If yes, does it mean that the frequency is modulated to distinguish between 1 carrier and 0 carrier?
    Since frequency in the PC is electric pulse,generated by a crystal, not magnetic pulse, the signals have +5V voltage, for example, in relation to what, an underlying carrier pulse voltage (frequency)?
    Does it mean that +5V signal strobe is by 5 counts higher than 0V signal strobe?

  2. #2
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    Huh? I'm not quite sure I understand your question, could you please claify it somewhat.

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    mjc
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  3. #3

    Post

    Originally posted by mjc:
    Huh? I'm not quite sure I understand your question, could you please claify it somewhat.
    Thank you, MJC.
    I think, I don't understand, how the system transforms a continious string of signals generated by the clock oscillator, into binary data signals (instructions, addresses, data - anything).
    The clock oscillator generates UNIFORM string of electric signals at a given pace - frequency (=signal genesis), so how they become 1s and 0s? Do they differ in voltage, and where does it happen? Clearly, not at the oscillator's output. Computer circuitry and components can only destinguish signals by the difference in their electrical properties. Also, a 0(binary) signal can't have a 0 voltage, otherwise it is not a signal. Equally unclear, how can you put 2 (or more, for that matter) bits of data on the rising (or falling) slope of the signal curve, if you don't know the physical characteristics of such signal, as opposed, for example, to the signal carrying only 1 bit of data, or the one that does not carry data at all (- do such signals exist, btw, with no data?). In other words, is there an explanation of what happens inside the circuitry at the physical level? "How did it happen, how it all began?". Or "forget about it?"

  4. #4
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    I believe it's called TTL (Transistor-Transistor Logic)

    > The clock oscillator generates UNIFORM string of electric signals at a
    > given pace - frequency (=signal genesis), so how they become 1s and 0s?

    The power supply provides the voltage : 5v = 1, 0v = 0

    If you have a 32-bit bus, then you have 32 wires with either 0v or 5v.

    The clock just provides a signal to tell the various components when to change.

    > Also, a 0(binary) signal can't have a 0 voltage, otherwise it is not a
    > signal.

    On the contrary 0v = binary zero. Take for example the letter 'a' - in ASCII (American Standard Code for Information Interchange) it is represented as the number 97 decimal or 0x61 in hexidecimal or 0110 0001 in binary. Now say you have 8 wires.

    5v ------+
    0v ----+ |
    Wire 0 +-|--- 0
    Wire 1 | +--- 1
    Wire 2 | +--- 1
    Wire 3 +-|--- 0
    Wire 4 +-|--- 0
    Wire 5 +-|--- 0
    Wire 6 +-|--- 0
    Wire 7 | +--- 1
    that gives you the ASCII character 'a'

    > Equally unclear, how can you put 2 (or more, for that matter)
    > bits of data on the rising (or falling) slope of the signal curve,

    I think you are confusing analog signals (radio, television, telephone) with digital signals (computers.)

    > Or "forget about it?"

    That too

    Grins --

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    [This message has been edited by spaceAlien (edited 07-09-2001).]
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  5. #5
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    -5v and 0v are binary one and zero and are generated within the power supply. They are transported by the signal bus if they are used as signals, the data bus as data, and the address bus as addresses.

    -Signals are not heterodyned onto the processor clock. There is in fact no intelligence on the processor clock at all.

    -There are no a frequencies which carry a 1 or a 0. These are DC levels. There is no modulation taking place as you're probably thinking of it.

    - A crystal does not generate a pulse, but a frequency at around .75 VDC. It is then amplified and then run through a clipping circuit to shave off the amplitude noise. It is clipped at about 5V AC to a square shape. The square shape then becomes ones and zeros all lined up, just itching to become data.

    I hope this helps.



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  6. #6
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    Talking

    darn, there goes my theory of the litle white rat in the roll cage!

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    iisbob
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  7. #7
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    real simple 1= on 0 = off.



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  8. #8
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    I think you want to look at simple 7400 logic chips. (look up 74AC04) They have connections to two voltages, 0V aka ground, and VCC, generally 5 Volts DC, but lately most devices run from lower voltages because they make less heat that way. Each "gate" is a set of transistors that alternately conduct current from/to iether power supply connection. When the transistor connected from an output pin to VCC conducts, it pulls that connection up to VCC, ie = a logic 1. When another transistor connected from that same pin to ground conducts, it pulls the output down to a logic zero. This pair of transistors is called a totem-pole output, and both transistors are never supposed to conduct current at the same time. You need a basic understanding of elecricity.

    A computer clock is created by a chip that alternately drives a wire to 1 and 0, 1 and 0 very fast. A 100 MegaHertz clock is a wire that is switched from 0V to VCC and back again in 10 nano Seconds, ie it spends about 5 nano Seconds at 0V and the remainder at VCC (5V, 3.3V, 2.5V, 1.8V...) The ratio of high vs low is called the duty cycle. Most chips in a modern Computer contain millions of transistors wired in a very complex logic.

    There are many layers to computer logic. Start with switch and light bulb logic and work your way up.

    Cheers,
    Steve

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  9. #9
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    In theory maybe you guys a correct.

    But in actuallity there are Little People
    cruising around in there.... hanging stickie notes.

    Busy Little People.





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  10. #10
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    Like digging up things?

    Generally a topic this old doesn't need any more replies, the original poster is long gone or it has become ancient history...

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    mjc
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    Celts are the men that heaven made mad, For all their battles are merry and their songs are all sad.
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    “When men yield up the privilege of thinking, the last shadow of liberty quits the horizon.” - Thomas Paine
    Remember: Amateurs built the ark; professionals built the Titantic."

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