Serial in parallel out shift register

[kpr123]

Hello everyone,

I am trying to design a serial-in parallel-out shift register for my 4-bit DAC. I tried simulating the following circuit but only the first few bits(serial in:01011)are shifting and the rest bits are disappearing. Am I missing something here?
Could someone please let me know what's wrong with it. It would be really helpful.
Thank you

 

[Pommie]

Are you asking why a four bit shift register only holds four bits?

Mike.

 

[kpr123]

No.
I was expecting something like this(attachment) in the output. Shifting of the input bits

 

[Pommie]

And, what are you seeing?

Mike.

 

[kpr123]

serial input data given here is 01011, But the output that's getting shifted is different than the input.

 

[Pommie]

It looks like there's something wrong with the first flipflop as d3 is wrong. Once d3 changes the change ripples through as it should. Double check the first flipflop.

Mike.

 

[JimB]

I take it that this is a simulator of some kind rather than real hardware.

The problem could be due to the relative timing of the clock pulses and the input data.

I suggest that you make the clock pulses narrower, say half the width that they are now, and, delay them slightly so that the clock edges do not correspond exactly with the data edges.

JimB

 

[Pommie]

Well spotted Jim. If the data is clocked on the rising edge then inverting the clock should also work.

Mike.

 

[kpr123]

Thank you@JimB. I tried what you said but the result is the same. kindly go through the image

 

[kpr123]

Mike I took the pos edged D flip flop with reset from the library itself. So I don't think there will be any problem with that.

 

[eTech]

No.
I was expecting something like this(attachment) in the output. Shifting of the input bits

I don’t know how accurate the DFF has been modeled, but they have a “setup time”. The D input has to be set BEFORE the rising edge of the clock.

eT

 

[Pommie]

If the clock is inverted then the data will be stable when the clock goes high. If it doesn't work then something else is wrong.

Mike.

 

[atferrari]

I have no time to do it myself but I would cheat checking the timing diagram of an IC doing that.

From the top of my head CD4094. Did lot of nice things with it.

Also 74LS595 maybe?