Re: [cosmacelf] Membership card latch signal
- bill rowe wrote:
> I tried using the out4 signal to latch the data from the output of theHi Bill,
> 74hc374 into a CD4021 shift register. The 4021 loads its output
> registers while its latch input is high and latches it when the signal
> goes low. This seemed ideal because the 374 loads on the leading edge.
> What I find is that the data loads fine when the out4 is triggered by an
> OUT 4 instruction but not when it's triggered by a dma/load cycle.
> Looking at the diagram I don't see why the two cases would be
> different. It's tough to see on a scope because the actual dma cycle is
> variably delayed from the input switch trigger.
> there should be just one out4 for each in switch shouldn't there?
An OUT instruction is a memory *read* cycle (with one or more of the N
lines also high). /MRD will be low, /MWR will be high.
A DMA-IN cycle (as used in LOAD mode) is a memory *write* cycle, with
/MRD high, /MWR low, and none of the N lines high. Thus, you won't write
to the output latch or your 4021 during the DMA-IN cycle.
But in LOAD mode, the DMA-IN cycle will be immediately followed by a
memory read cycle. This second cycle is the one that latches the data in
the output latch.
Where exactly are you picking up the signal to control your 4021? There
is a rising edge on pin 11 of the 74HC374 whenever data is written into
it, regardless whether it is from an OUT instruction or LOAD DMA-IN
The 74HC374 is *edge* triggered (latches at the rising edge of pin 11),
while the 4021 load pin is *level* sensitive. Try an RC differentiator
(series capacitor from 74HC374 pin 11 to 4021 pin 9, resistor from 4021
pin 9 to ground). With this, the rising edge momentarily pulls 4021 pin
9 high, but then it goes back low no matter what 74HC374 pin 11 does.
Anyone who has never made a mistake has never tried anything new.
-- Albert Einstein
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
- I have one of these that has worked out well.
--- In email@example.com, Andrew Wasson <awasson@...> wrote:
> Yup, All you have to do is read the first couple of sentences (http://www.saleae.com/counterfeit) to realize who is impacted by the pirated pieces. I'll build my own or save my pennies to buy the real McCoy. I'm glad Josh did the research and posted it before I got around to buying one too.
> On 2013-07-19, at 6:29 PM, Lee Hart <leeahart@...> wrote:
> > Steve Gemeny wrote:
> > > Josh, I applaud your integrity on this.
> > Same here! We all know how much work it is to create something; a
> > circuit, or program, or any other new and useful thing. And, we know how
> > much it would bother us if someone stole our work and were selling it at
> > a ridiculous price. Patents and copyrights are essentially worthless.
> > That, coupled with the anonymity of the internet makes it easier than
> > ever to sell pirated goods.
> > It's difficult to resist a really cheap price. It takes real character
> > to decide when a bargain is in fact too good to be true, and turn it
> > down. But, that's the only way to stop these modern-day pirates.
> > --
> > Never doubt that the work of a small group of thoughtful, committed
> > citizens can change the world. Indeed, it's the only thing that ever
> > has! -- Margaret Mead
> > --
> > Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm