At 10:36 06.09.2002 -0800, you wrote: >I haven't touched NMOS in ages (if ever) so I'm certainly no expert ... >but one might think that they all might have been designed with the same >(TTL) thresholds. I suppose that would be wishful thinking.
NMOS and CMOS are somehow interchangable, but the problem is the slow rise and fall times of NMos. Some CMOS circuits react with flaky outputs during the transition. If you clock a CMOS counter with an NMOS signal, it might clock several times during the transition. The more noise you have on GND, the more clocks you get. When I designed the "Retro Replay" for the Commodore C64 (see ar.c64.org), I had tons of problems like this: I had to handle up to 0.7V noise on GND, and transition times of up to 50ns. I first solved this by adding schmitt-triggers, later got rid of them by routing the critical signals through RS-flipflops inside the MACH210 chip. You don't find solutions to problems like this without proper measuring equipment. A simple 16-channel logic analyzer for the PC will do, but it's always good to have the possibility to sample an analog channel over the same period. My personal recommendation is the Agilent mixed-signal scope series (especially for the good price/performance relation), but Tektronix may have even more sophisticated equipment. Maybe I can afford one.. one fine day :-) ciao, -- Jens Sch�nfeld -- Author: Jens =?iso-8859-1?Q?Sch�nfeld? INET: [EMAIL PROTECTED] Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
