Tim's own version of the Catweasel/Compaticard/whatever

I agree that the device in question doesn't offer OC/OD outputs, a tristate driver would work as well, and the CPLD drives a bit MORE (8 mA) than the typical HC/HCT device (6 mA). I think the CPLD would provide an easy-to build alternative that would require some assembly, but which could be modified without wiring or soldering/. If you look at FDC's used in many systems, including some of the ones used in PC-clones, didn't bother with OC drivers. It's not critical unless you have more than one controller on the cable. That happens rather seldom. HCT's by the way, don't have open collectors. In fact, they don't have collectors at all. It doesn't matter, though. If you drive a line with a tristate buffer with the appropriate polarity at its input, it will behave pretty much as an OC device does, only better and faster. If you don't believe that, try plugging a 74126 with an input grounded into a circuit prevously occupied by a 7403. of course it must be wired such that the logic functions the same, but it's a valid comparison. The more common 7438 is not valid for comparison because they didn't get around to building a tristate buffer in the '126 pinout. When you hit the enable with a high, the output will go low, lickety-split, just like the OC. You'll need a pullup in either case. Dick ----- Original Message ----- From: Chuck McManis <cmcmanis(a)mcmanis.com> To: <classiccmp(a)classiccmp.org> Sent: Wednesday, July 05, 2000 12:48 PM Subject: Re: Tim's own version of the Catweasel/Compaticard/whatever