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Packet Transfer; Clock Cycles

  1. Jul 31, 2003 #1
    I observed with several electronic devices (primarily romote controls) which use infrared light emitting diodes (IR-LEDs) to send data is that with some, if the LED is viewed closely and carefully enough you can see a red light flash when being used. I know that IR light is invisible, and I'm not looking at it through a video camera or some special optical device, so I assume that the fact that I can actually see a tiny light must be based on the fact that the LED isn't perfect and therefore, some visible light is emitted along with the infrared light. And now that I think about it, the fact that the light looks red is understandable as infrared is just below the red light of the visible spectrum. Anyway, the thing about IR-LED's is that the light coming from them looks rather fuzzy, like it's flashing on and off quickly. I have an iPaq Pocket PC (H3800 series) that has infrared data transfer capabilities. And when it's transfering data via IR it periodically lights up a fuzzy red for about a second and then stops for about a second. The process is repeated over and over again.

    My question concerns this flashing (on/off) mechanism. I know that all information in a computer is in the form of the pulse (1) and absence (0) of electrical discharges, which represent binary digits (zeros - ones). And the binary digits are grouped into "bits" of information (16 bit, 32 bit etc) to represent ASCII (American Standard Code of Information Interchange) characters which make commands to the hardware. I read a while back about processor types and speeds of PDAs (Personal Digital Assistance). Of course, the processor of a handheld device is less sophisticated and cutdown but still similiar. The processor type installed in my Pocket PC is an ARMStrong, which is 206MHZ. Processing speed is measured in "clock cycles." So put in another way, a light flashes so many times within a second to send whatever quantity of bits of information, and after the second is up it pauses and then initiates another packet transfer (repeats the process)? Microprocessors have timers inside them. So the on and off correspond with the 1 and 0 binary digits. And megahertz (MHZ) must be a measurement of how fast the processor can read within a second? If this is correct then it means that my Pocket PC can read 206 million binary digits in one second?
     
  2. jcsd
  3. Aug 1, 2003 #2
    You have soooo many questions..... tell me if I skipped something important, or if you need extra info :smile:

    "And the binary digits are grouped into "bits" of information (16 bit, 32 bit etc) to represent ASCII (American Standard Code of Information Interchange) characters which make commands to the hardware"
    actually ASCII characters have 8 bits and are not related to commands to the hardware. The processor uses instructions which usually have 32 bits and are coded by the producer. ASCII characters are just a way of representing the information....

    "Of course, the processor of a handheld device is less sophisticated and cutdown but still similiar"
    not necesarilly. The processor of a handheld device can have many features that a normal processor does not use (example: power-saving)

    "And megahertz (MHZ) must be a measurement of how fast the processor can read within a second?"

    For every clock cycle a processor performs one instruction. A instruction can mean "read 32 bits from memory" or "add register A with register B and store result in memory". A processor doesn't spend all his time reading data, it must process also.

    "If this is correct then it means that my Pocket PC can read 206 million binary digits in one second?"

    The speed of communication between two devices does not depend upon the processor clock. It has to do with the network protocol, the devices used for communications and some other parameters. I'm sure if you look at the databook of your Packet PC, or on the net you could find the rate of transfer.
     
  4. Aug 1, 2003 #3

    russ_watters

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    Staff: Mentor

    The data transfer rate of irda devices has nothing at all to do with the clock speed of the central processor. Otherwise irda devices would all run at different speeds and wouldn't be able to talk to each other. All such devices in a computer follow industry standards, in the case of irda devices, the vast majority run at 9600 bps (bits per second) and are controlled by their own internal hardware (chips).
     
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