Data Frames.

Discussion in 'General Electronics Chat' started by cjdelphi, Sep 21, 2010.

  1. cjdelphi

    Thread Starter New Member

    Mar 26, 2009
    272
    2
    I'm going to try and explain my understanding so I can be corrected, I always figured to talk from 1 IC to another IC let's say over a serial cable here, the transistor turns on, sends a voltage down the cable, the IC then reads 1, then off goes the transistor then becomes 0.

    How's it keep in sync? does it simply only trigger with voltage, so if we sent hello in binary A is 65 now i have to use my brain, 65 in binary becomes 1000001 so the transistor switches on... then off, then what?... in order to send that data frame, it would have to send On, off (no voltage) but you can't then resend no voltage so there's something to keep them in sync right?..

    Let's suppose each IC was timing every second, it could send 1 bit of data, the other IC would say in this 1 second i got either 1 or 0, but a 1 hert cycle does not sound very accurate, what if at the time it sends the data the other IC is not listening IC 1 listens at 1 second but the 2nd IC listens at 1.2 seconds (it wont see anything)...

    ok so let's take it up from 1 second cycles to 10ms cycles, or 1ms or 1ns, am right in assuming that there's some point in time that you're able to sync because there's really not much between them or is it all down to a sync procedure which goes, start now listening every 1 second so they both fire off at 1 second or is it down to raw speed in that every 1ns is the same as 1ns everywhere else in the world because it's so fast?..

    IF you see what i'm getting at... basic communications from a frame on a hardware level using transistors or is there more to it?...
     
  2. Dyslexicbloke

    Active Member

    Sep 4, 2010
    420
    19
    You need to separate in your mind the physical layer from the protocol.

    There are hundreds of protocols, some synchronous some not, how these are implemented physically will vary from device to device but will conform to some standard.

    Have a look for I2C or CAN bus as both were originally designed with chip to chip comms in mind.

    Compare them to RS-232 and RS-485.
    Note that the electrical and timing requirements are specified but how these are achieved is left entirly up to the designer.

    Hope this helps
    Al
     
  3. tom66

    Senior Member

    May 9, 2009
    2,613
    214
    Some protocols transmit a clock signal which tells the receiving device when to grab the data bit.

    Other protocols encode the clock with the data, in a form of encoding known as Manchester encoding.
     
  4. cjdelphi

    Thread Starter New Member

    Mar 26, 2009
    272
    2
    ah hah, the Manchester Encoding is probably the best example i've seen (i've been googling a fair bit found nothing of real use to explain it) but this Manchester Encoding seems to be exactly what I was trying to get my head around... thanks

    :)
     
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