serial transfer of data

Discussion in 'General Electronics Chat' started by anhnha, Jan 22, 2013.

  1. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    I want to know about serial transfer of data. For example, I want to transfer data between two computers; one is transmitter and the other is receiver. The distance between them is about three metres. the baudrate is 9600bps, therefore the time needed to transfer one bit is about 0.1ms. When one byte is transmitted, is it true that the first is transfer through the line and until the receiver received it (after 0.1ms) then the transmitter continue to transfer the second bit?
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    That is correct. To transmit eight bits, you need to transmit also a start bit and a stop bit for a total of ten bits. Hence the total time for transmission is 1ms.
     
  3. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    Thank but i want to know how each bit is transfer. Is it true that after receiver receive the first bit then the second will be sent? My leturer said that the second bit is transmited while the first bit still in the line and the receiver has not received the first bit. That confusing me.
     
  4. MrChips

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    Oct 2, 2009
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    The transmitter does not know whether or not the receiver has received the bit.
    The transmitter is like someone controlling the power switch of a light bulb. The bulb is turned ON or OFF for 0.1ms.

    I would say your lecturer is wrong. It is not like cannon balls in a cannon waiting to be fired out.

    What he means is that serial transmission can be implemented using a shift register (SR). Data is shifted out from the transmitter SR into the receiver SR. It takes one clock delay to shift the bit from the transmitter SR to the receiver SR.
     
  5. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    Well, thank! I think what you said is here:http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/datatran2.html
    But how about the case I said in original post? Is it true that the transmitter will transmit
    each bit after 0.1ms at baudrate 9600bps.
     
  6. MrChips

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    Like I said, each bit is left on (visible to the receiver) for 0.1ms before changing to the next bit.
    It is like showing flash cards for a fixed length of time.
     
  7. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    Thank you for clearing up my doubt. It is what I want to know. Yesterday, my class discussed about the speed of data transfer between serial link and parallel link. With assumption that both methods have the same baudrate and my lerturer said that the serial has higher speed, therefore, now in computer many devices have transfered from parallel to serial transmission.
     
  8. MrChips

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    A parallel interface has higher data throughput than a serial interface.
    It is like a multi-lane highway vs a single lane road.

    A serial interface uses a cable and connector that has fewer wires and connections.
    A single lane road is cheaper to build than a multi-lane highway.
     
  9. Brownout

    Well-Known Member

    Jan 10, 2012
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    Serial comm has overtaken parallel methods for speed. Ethernet can transfer data at 10G bps. Some serial buses can transfer data over multiple "lanes" which multiplies the aggregrate data rate. PCIe is one such example.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    One of the reasons serial has overtake parallel for high transfer speeds is the problem of skew in parallel data buses. As the frequencies get higher, maintaining the skew between the parallel bits to less then one bit length becomes problematic, due to various uncontrollable differences in transmission speed and circuit delays, and data errors start occurring. This is not a problem with serial transmission. You can transmit the data at as high a speed as you can get the serial bus to transmit a reliable one and zero.
     
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