On Mon, 27 May 2002, Dwayne Reid wrote:

> >Russell McMahon wrote:
> >
> >  I have now gone to a 4040 counter with a naughty two diode and resistor "AND
> >  gate" to drive the reset. Resistor from RESET to Vcc. Diodes from Q1 and Q3
> >  to RESET (Anode ends). When both outputs are high the diodes block, resistor
> >  pulls up reset line and both Q's fall again. The resultant reset pulse is
> >  therefore "just long enough:" to cause reset and has the potential to only
> >  partially reset the IC. As I am using just the first two stages the chances
> >  for erroneous operation MAY be reduced compared to higher divide ratios.
>
> This should be reliable.  But you can eliminate 1 diode - use the resistor
> in place of the diode.  If you think about it, you wind up with the same
> logic.  The pin with the resistor has to be HI before the reset can occur,
> the pin with the diode also has to be HI or it is still clamping the reset
> pin LO.  In other words, 1 resistor and 1 diode makes an AND gate.
>
> dwayne
>
  In CMOS tehnique you may use also capacitors for AND or OR as derivative
choice. The only problem is to not have trust in the input internal
protection diodes.

regards, Vasile

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