Shift registers how is serial data converted to serial out....

Discussion in 'General Electronics Chat' started by nepdeep, Jan 21, 2013.

  1. nepdeep

    Thread Starter Member

    Sep 14, 2011
    139
    0
    Hi , I studied about serial in serial out shift registers. Yes when followed the steps sequentially, it does so...but eg. if i input 1011 at serail in....i would get 1000 the first time
    1100 the second time
    0110 the third and
    1011 on the fourth time only.

    Now my question is...the data is seen only after four clock cycles...and untill then...till three cycles...wrong data is seen....untill three clock cycles...so how do we give just the fourth data out ....and prevent the first three datas...from being outputed...?
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,446
    3,362
    That is not how serial shift registers work.
    The serial output only reveals one bit at a time.
    What do you mean by "the data is seen only after four clock cycles"?
    After four clock cycles, the serial output is 1.
     
  3. tshuck

    Well-Known Member

    Oct 18, 2012
    3,531
    675
    I think you mean a serial to parallel shift register? Otherwise, as MrChips has stated, you will have either a 0 or 1 on your output at any one point in time.

    If you are meaning a shift register with parallel output, then the output cannot be prevented from changing while data is shifted in. What you can do, however, is to get a shift register with output latches, which allow you to latch data to the output after X clock cycles. So the external circuit would only see transitions from previously valid data to valid data....
     
  4. nepdeep

    Thread Starter Member

    Sep 14, 2011
    139
    0
    I think i have been mistaken ...I was thinking like packet shifting...so what actually is this shifting helping then...please help me get over with shift registers .. ;)
     
    Last edited: Jan 22, 2013
  5. MrChips

    Moderator

    Oct 2, 2009
    12,446
    3,362
    Let's start from square one. What are you trying to do?
     
  6. nepdeep

    Thread Starter Member

    Sep 14, 2011
    139
    0
    Mr Chips...I am tyring to find out how can we use serial in serial out shift registers....may be you can give simple example to begin with and then We can go on...thanks in advance
     
  7. MrChips

    Moderator

    Oct 2, 2009
    12,446
    3,362
    Funny thing is an application for serial in, serial out shift register does not immediately come to mind, except as a digital signal delay, used in encoders, random number generators and DSP applications.

    There are many applications for serial in, parallel out and parallel in, serial out.
     
  8. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    Maybe your´re mixing this up with a FIFO? I don´t see any purpose to a pure serial in, serial out shift register, apart what mrChips said.
     
  9. tshuck

    Well-Known Member

    Oct 18, 2012
    3,531
    675
    Perhaps you are thinking of two shift registers that shift data to each other? I could understand why you might think that the shift registers in a microcontroller could be considered serial-in-serial-out shift registers....

    Otherwise, this would function as a digital signal delay..
     
  10. nepdeep

    Thread Starter Member

    Sep 14, 2011
    139
    0
    hmmm...i have to do liittle research before talking to you guys now... :) I am not that far to the DSPs yet... :)
     
  11. tshuck

    Well-Known Member

    Oct 18, 2012
    3,531
    675
    Aside: (Actually a DSP usually refers to a specific to s specific type of device, a microcontroller, while able to be considered a DSP, is more generic, not having specialized hardware for DSP functions)

    Sorry, I wasn't intending to confuse you, just to clarify what you are referring to so that we might understand your dilemma...

    As an example of your serial-in, serial-out shift register, let's say you have a 8-bit shift register, then as you shift data in, you will only begin to see the correct data beginning 8 clock cycles later...
     
    nepdeep likes this.
Loading...