Loading ...
Sorry, an error occurred while loading the content.

RE: [cosmacelf] Membership card latch signal

Expand Messages
  • bill rowe
    ... ok. so there could be a delay on the order of 16 to 48 cycles between pressing in and having the data latched. ... Yes, I m picking it up at pin 11 of the
    Message 1 of 31 , Jul 17, 2013
    • 0 Attachment
      > 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.
      ok.  so there could be a delay on the order of 16 to 48 cycles between pressing in and having the data latched.

      > 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 
      > operation.
      Yes, I'm picking it up at pin 11 of the hc374.  I was using this signal directly figuring that it had to go low "fairly quickly" but even if I wait 200 us before shifting the 4021 i get garbage.  Josh's logic analyzer would come in handy.

      > 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.
      I'll try this now.  I guess it won't interfere with the C6 delay, if I use an 82pf cap and a 22K rx I'll get a couple of us pulse.



      > To: cosmacelf@yahoogroups.com
      > From: leeahart@...
      > Date: Tue, 16 Jul 2013 23:44:51 -0500
      > Subject: Re: [cosmacelf] Membership card latch signal
      >
      > bill rowe wrote:
      > > 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?
      >
      > Hi Bill,
      >
      > 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
      > operation.
      >
      > 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
      >
      >
      > ------------------------------------
      >
      > ========================================================
      > Questions? Check the FAQ at http://www.cosmacelf.com/forumfaq.html
      > Visit the COSMAC ELF website at http://www.cosmacelf.comYahoo! Groups Links
      >
      > <*> To visit your group on the web, go to:
      > http://groups.yahoo.com/group/cosmacelf/
      >
      > <*> Your email settings:
      > Individual Email | Traditional
      >
      > <*> To change settings online go to:
      > http://groups.yahoo.com/group/cosmacelf/join
      > (Yahoo! ID required)
      >
      > <*> To change settings via email:
      > cosmacelf-digest@yahoogroups.com
      > cosmacelf-fullfeatured@yahoogroups.com
      >
      > <*> To unsubscribe from this group, send an email to:
      > cosmacelf-unsubscribe@yahoogroups.com
      >
      > <*> Your use of Yahoo! Groups is subject to:
      > http://docs.yahoo.com/info/terms/
      >
    • Chris
      I have one of these that has worked out well. http://dangerousprototypes.com/docs/Logic_Sniffer_quick_start_guide
      Message 31 of 31 , Jul 20, 2013
      • 0 Attachment
        I have one of these that has worked out well.

        http://dangerousprototypes.com/docs/Logic_Sniffer_quick_start_guide

        http://www.epictinker.com/Open-Workbench-Logic-Sniffer-p/obc101e1p.htm

        C.W.







        --- In cosmacelf@yahoogroups.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.
        >
        > Andrew
        >
        >
        >
        >
        > 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
        > >
        >
      Your message has been successfully submitted and would be delivered to recipients shortly.