So where's the rest of the 74HC family?

They are still available, maybe not as easily as they were a while ago. Try the HC192 or HC390. Digikey has them.

But I don't think HC will solve your problem. Even the simple HC74 only goes at 25 MHz at 4.5V over temp. You might squeek through if you keep the voltage up keep it cool.

Have you considered one of the cut-to-order osc places? In the old days they would actually make crystals to any frequency reasonably quickly. Now you can get osc packages that have a PLL and are programmed to order. The downside is jitter from the PLL which might matter if you are running an A/D.

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1) Why does a uC need a VCO? 2) 3.6MHz sounds close to the NTSC colorburst of 3.579545 MHz 3) No one uses discrete logic much anymore. If they do, it's in a hand-unusable package.

Answers:

1) Ever hear of "disciplined oscillator"? This uC keeps itself slaved to a remote system. 2) The numbers you cite are indeed close to each other. Surely you don't mean to imply that a 3.6 MHz crystal is a direct replacement for a color burst crystal. 3) On the contrary, I use discrete logic, and this uC is in a handheld package.

School's over now.

--
Michael

1) You could have said so. Why where you going on and on about crystals and dividing down frequencies if the voltage CONTROL part is important? 2) No, I meant the reverse. That is what you were asking for right? You want to replace a 3.6 MHz VCO with a crystal? Why would you think I implied 3.6MHz is a replacement for a color burst? I said the reverse. The other way around. Reverse. 3) I meant packages are so tiny you can't see them. You know, the actual part itself, the package. Like DIP or SOIC. Package. Tiny. Assemble by hand you do not.

Recess is over now.

In which case it probably does timekeeping by tweaking a drift rate and counters inside the microcontroller.

I'm still confused as to what you're writing about, "Crystal" and "VCO" are not necessarily exclusionary concepts but now you're throwing in microcontrollers too.

Do you actually need (maybe) a 3.6MHz VCXO module? Or a little LC oscillator with a varactor?

No, it isn't, but I've seen 3.579545 MHz crystals labeled "3.6" especially in surface mount where you don't have a lot of room to stick all those digits :-).

Digikey does stock 7.2 MHz crystals BTW. And if you're looking for

4-bit counters you will probably end up with slightly-higher integration HC393's, HC390's in async or HC161/HC163 sync counters today. A couple counters and a 74HC4046 PLL/VCO/phase detector can let you synthesize almost any frequency out of any other if worse comes to worse.

Jameco has a pretty good selection of older 7400 families etc.

Tim.

VCO?

one uses discrete logic much anymore. If they do, it's in a

package.

keeps itself slaved to a

In which case it probably does timekeeping by tweaking a drift rate and counters inside the microcontroller.

I'm still confused as to what you're writing about, "Crystal" and "VCO" are not necessarily exclusionary concepts but now you're throwing in microcontrollers too.

Do you actually need (maybe) a 3.6MHz VCXO module? Or a little LC oscillator with a varactor?

other. Surely you don't mean

replacement for a color burst

No, it isn't, but I've seen 3.579545 MHz crystals labeled "3.6" especially in surface mount where you don't have a lot of room to stick all those digits :-).

Digikey does stock 7.2 MHz crystals BTW. And if you're looking for

4-bit counters you will probably end up with slightly-higher integration HC393's, HC390's in async or HC161/HC163 sync counters today. A couple counters and a 74HC4046 PLL/VCO/phase detector can let you synthesize almost any frequency out of any other if worse comes to worse.

Jameco has a pretty good selection of older 7400 families etc.

Tim.

I would be very critical of just being able to plop in "any old" 3.6MHz crystal in this place, much less one at a multiple of the frequency. The rubber (pullability) you get with a crystal is very dependent on multiple crystal parameters, not just frequency.

If you can characterize the VCXO part of the flaky crystal in-circuit (e.g. 3V change in control gives 20ppm shift) you'll have better luck at least testing your replacement.

Just because the crystal quits oscillating above some temperature doesn't necessarily point the finger at the crystal - any part of the oscillator might have gain depend on temperature. I would finger the semiconductors before the crystal. Any polypropylenes in that oscillator? If they've ever been above 85C they can start giving very odd symptoms.

yesterday

Their website is very nice for such searches.

Is it vaguely possible you can find a "parts" unit for stripping out a crystal?

Tim.