Flip-Flop in LTSpice, set/reset assertion?

On Monday, September 23, 2019 at 10:07:10 AM UTC-4, Joerg wrote:
> On 2019-09-22 18:36, Gerhard Hoffmann wrote:
> > Am 22.09.19 um 16:21 schrieb Joerg:
> >> On 2019-09-21 13:53, Gerhard Hoffmann wrote:
> >
> >> Old TTL didn't pull very high. 3.5V to 4V in some cases so noise
> >> immunity was indeed worse, until CMOS came. That made things
> >> cumbersome because you could not use OC structures to operate it from
> >> external.
> >
> > TTL levels have nothing to do with 5V. That is just the supply voltage.
> > The switching threshold is somewhere near 1V8, anything below 0V6 is
> > definitely low and anything above 2V4 is definitely high.
> >
> 
> And sometimes the drive signal didn't quite get there. Or not all the 
> time. The threshold in TTL is lower though, but occasionally it wasn't 
> low enough. Unless you used 244 bus drivers this stuff just didn't have 
> any oomph.
> 
> 
> > CMOS has its threshold at 1/2 VCC, but the historic importance of
> > TTL required the extraneous 74HCT family with the lower TTL input
> > threshold, implemented by playing games with the width/length ratio
> > of the FETs.
> >
> 
> That is one reason I was never much of a fan of HCT. In my youth I built 
> a lot of circuits with CD4000 logic because it didn't have such 
> problems. It had other problems but the main upside was a vastly lower 
> power consumption.
> 
> >
> >>> And no, modern digital design has nothing to do with deploying 74xxx.
> >>> You formulate your system in VHDL, Verilog or Matlab and that's it.
> >>> Nobody cares about flipflops, let alone their reset pin polarity.
> >>>
> >>
> >> Nobody? Really nobody? Way north in France, in the province of the
> >> Gauloises ...
> >
> > Deploying a few gates is not digital design.
> >
> 
> That part fulfills logic funtions. If this and that happens at the same 
> time tug on an alert rail, otherwise not. Preferably while consuming 
> less than 1uA. What's not digital about that?
> 
> 
> >> For example, right now I have to design a circuit for a device that
> >> replaces a uC function because the uC can't be trusted to do the job
> >> reliably enough. I think it could be made reliable but a client's wish
> >> is a client's wish. It'll need several 74LVC chips.
> >
> > Consultant's creed:
> > It's our policy to give the customer what he wants.
> > That is very strong medicine, and usually only required once.
> >
> 
> :-)
> 
> Once is the goal, of course. After that I (and the client) expect this 
> to run for the next few decades.

Whoosh!

-- 

  Rick C.

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