D Flip Flop in Simulink

[James Laudolff]

Hello,
I tried a simple simulation in Simulink with two clocks and two D flip
flops and found that only one of the flip flops seemed to be
functioning. The flip flop models are from the extrflip library. I am
checking the outputs on a scope and have fiddled with the max step and
tolerance parameters. Any ideas?

I checked the MathWorks web site and found that the JK flip flop model
is unreliable is this the case for the D model as well?

I have just started using Simulink and am trying to see if it is useful
for modeling phase-locked loop transients to investigate lock-time. I
have used Matlab successfully in the past to model linearized control
systems.

Thanks,
Jim Laudolff
laud...@cae.cig.mot.com

[neric]

James Laudolff wrote:

> I tried a simple simulation in Simulink with two clocks and two D flip
> flops and found that only one of the flip flops seemed to be
> functioning. The flip flop models are from the extrflip library. I am
> checking the outputs on a scope and have fiddled with the max step and
> tolerance parameters. Any ideas?

I also find some of the Simulink Blocks unreliable (or maybe not
well-documented) that I usually use the Matlab Function Block so I have
more control on the model. D Flip-Flop is one of them since the edge
triggling is a bit confusing.

A delay is required for the feedback if a self-written model is used.
At a given sampling time, the function input time is equal to the
fucntion output time.

I don't know if I am answering the question, but I hope this help.

[Robert Paynter]

For the phase-locked-loop problem, look for
the VCO block in the user contributed files.
/contrib/simulink/vco/

This is part of the README.txt file
..The VCO block can be used to model a phase-locked loop when used
in conjunction with a low-pass filter and a phase-detector. An
example of this implementation is included in this directory. ...

Robert Paynter, Elec Eng Imperial, London