Re: [cosmacelf] Membership card latch signal
- Josh: it's on my watch list - thanks.
On 2013-07-16, at 8:38 PM, "Josh Bensadon" <joshbensadon@...> wrote:Hi bill,
I bought a cheap Mini Logic Analyzer from Saleae (actually it's a cheap clone). Delivered for about $25. It's been absolutely worth every cent!
It only samples up to 24Mega samples per second, but that's enough for a 40nSec resolution. You get to see everything going on.
There's one for sale right now on ebay, 141017549206. They come often so don't bid high.
I bought mine from Alibaba.com. But from what I read on another forum, it's a crap shoot to buy through them.
Then again, for $20 bucks, you're not risking a lot. Mine came in the usual 4 week from China time frame.
There's actually many clones of the same device. I will guess they all work. I use the word Saleae in my search.
From: bill rowe <bill_rowe_ottawa@...>
To: "firstname.lastname@example.org" <email@example.com>
Sent: Tuesday, July 16, 2013 4:41:36 PM
Subject: RE: [cosmacelf] Membership card latch signal
I tried using the out4 signal to latch the data from the output of the 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?
Date: Thu, 6 Jun 2013 18:44:31 -0500
Subject: Re: [cosmacelf] Membership card latch signal
bill rowe wrote:
> *Lee: Could you explain the timing of the latch signal OUT4 on the
> membership card? If I want to load the output of the latch into another
> IC, will it be stable by the trailing edge of the N2 signal?*
Yes. During an OUT4/5/6/7 instruction when TPB goes high, flip-flop U5A
sets. Its high output on Q pin 1, triggers the 74HC374 output latch to
latch the data.
C6 is a slowdown capacitor. It delays the rising edge that latches U7
just a little bit. It's there because the RAM is also chip selected by
the rising edge of TPB. The capacitor allows for the RAM's access time.
And why is the RAM not chip selected until TPB? Old slow RAMs needed to
be chip selected as early as possible; usually at the end of TPA when
the address first becomes stable. New RAMs are very fast; but they
aren't true CMOS -- they draw power whenever their chip select pin is
low. So to minimize power, the RAM is chip selected as late as possible,
to minimize the time it is active and drawing power.
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
- I have one of these that has worked out well.
--- In firstname.lastname@example.org, 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