On Thursday 08 October 2009, Kirk Wallace wrote: >On Thu, 2009-10-08 at 10:15 +0100, Andy Pugh wrote: >... snip > >> I did these sums last night and came to much the same conclusion. I >> will see what I have in the way of buffers (I definitely have some >> Op-Amps I can configure in voltage-follower mode, but I will see what >> the 74LS255 is) > >... snip > > >74LS244 Data: >http://media.digikey.com/pdf/Data%20Sheets/Fairchild% >20PDFs/DM74LS244.pdf >(Short URL) http://preview.alturl.com/kjp9
That one I'm fairly familiar with. The LS means low power, and somewhat slow, schotkey type logic. Its faster than plain TTL but its output drivers aren't much better. The ALS244 might be a better choice as I believe its output drivers are stronger, better pullup to the logic one state. >I haven't studied the different logic families, so a 74HC244 or HCT or >other, might be better. The 4000 series logic can work with 12 or 18 >Volts, if needed. > Believe it or not, I once ran a couple of the 4xxx family at 28 volts, looking for some speed. It ran just warm enough to tell it was on, < 20F above ambient, switched in about 20ns, and ran that way for several years. I was putting colorized borders on the characters of a rather elderly character generator. TV stuff IOW. >The 74LS244 enables can help with blocking the state of the parallel >port as the PC boots up. EMC2's watchdog or rather charge pump feature: >http://linuxcnc.org/docs/2.3/html/man/man9/charge_pump.9.html > >can be used to keep the chip from passing signals until EMC2 is up and >running. My problem is that I have yet to get a stand-alone charge pump >detector working. This worked once, but failed when I tried to make the >final board: >http://www.wallacecompany.com/machine_shop/Shizuoka/watchdog-1b.png > >I think I just need to put more effort into understanding how it works >in order to adjust the component values. > >For inverting signals, I have used a 2N3904 or 2N2222: >http://www.wallacecompany.com/machine_shop/Shizuoka/watchdog-1b.png > >to sink a signal to ground. > -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The NRA is offering FREE Associate memberships to anyone who wants them. <https://www.nrahq.org/nrabonus/accept-membership.asp> "Anyone who is capable of getting themselves made President should on no account be allowed to do the job." - Some wisdom from The Book. ------------------------------------------------------------------------------ Come build with us! The BlackBerry(R) Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9 - 12, 2009. Register now! http://p.sf.net/sfu/devconference _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
