seems that your circuit is powered by the high-level data inputs (HC/HCT logic ICs have got ESD protection diodes to GND and Vcc at the inputs). So Vcc does not go down to (nearly) zero volts when you turn off the +5V supply. Anyhow I would prefer to have Schmitt-trigger gates at the inputs. that can solve a lot of problems with slow risetime. A special reset-controller (MAX705 etc.) which generates a clean reset signal, when the Vcc falls e.g. below 4 V, will be very helpful too.
regards Alois > At 17:54 09.01.2003 -0800, you wrote: > >Update: I found the problem. I was using Pericom's 74FCT521 with TI's > >74HCT164's. I changed it all over to TI's HCT devices and it works > >now. It's kinda odd though, I always thought FCT and HCT devices would > >work together. > > They should, yes. > > I'm not sure if this was the real cause of your fault. I think this is a > typical setup&hold problem. If your combinatorial input to the shift > register is not stable for so-and-so many nanoseconds before and after the > rising edge of the clock signal, you get nearly random results. This is > true for all kinds of flipflops - make sure that the input signal does not > change for a time window around the rising edge of the clock signal, and > all your problems are gone. > > >Here is my next problem though... when I power on the circuit, there is a > >resistor/cap on the clear line of the '164's. This resets the outputs to > >low on power on. When you power on the circuit with a high input to one > >of the channels, the analyzer is stuck with = high and never goes > >low. I'm thinking I need to apply one clock cycle to the '164 on power > >up, and after the power on reset??? > > > >any ideas? > > The '164 has an async clear, independant of the shift input(s), and > independant of the clock line. No idea what might cause this effect. > Checked all powers? Caps near parts? "ringing" or overshoot on clock lines? > Anything else causing glitches? > > ciao, > -- > Jens Sch�nfeld > > -- > Author: Jens =?iso-8859-1?Q?Sch=F6nfeld?= > INET: [EMAIL PROTECTED] > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com > San Diego, California -- Mailing list and web hosting services > --------------------------------------------------------------------- > 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). > - - - - - - - - - - - - - - - - - - - - - - - - - - Alois Bauer WORK Microwave GmbH Raiffeisenstr. 12, D-83607 Holzkirchen, Germany Tel. {+49} (0)8024-6408-0 / FAX (0)8024-640840 -- Author: Alois Bauer INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- 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).
