Hi, On 17 Mar 99 at 10:24, Dave VanHorn wrote: > >> First, is it a paralell resonant crystal? It must be, or you will > >> never get to sing the right tune, if it sings at all. > > >This isn't exactly correct. If the crystal is specified for a serial > >oscillator it should run fine in a parallel one but slightly off > >frequency (typically about 0.02% above its specified frequency). > > > We may be saying the same thing here, but I'll re-state. A series rock > WILL NOT run at the specified frequency in a paralell circuit. It MAY > operate, but it will be at a different frequency, and it may refuse to > start at all. I have seen series rocks that couldn't be made to > oscillate with a microprocessor. (that was the major clue that someone > bought the wrong rocks) I have not researched this issue personally but all the literature I have (from crystal and silicon manufacturers) says the series rock will oscillate just as well but a tiny bit off frequency (the series resonant frequency). There is no physical difference between those crystals. It's just that parallel resonant crystals are specified for a certain load and frequency. I can give you specific references if you like. > Typical values are better than nothing, but I hear SO many people with > similar problems.. Trying C after C, yet loading the xtal with the > specified load cap (and having a paralell resonant xtal) has NEVER > failed me, even in production of millions of units. I am willing to bet 99.9% of these people didn't get oscillations for other reasons. I used to work with this guy who would just pull out caps from his "small pf" drawer without knowing their values and stick them on the various circuits we made (generally 4Mhz-50Mhz). Never once did any of these circuits not oscillate. We also never used a series resistor.. . However, when you work with low freq. watch crystals it's a whole different ballgame... Some years ago I've made a design around a TI C50 DSP which would not run. After finally getting through to TI's tech support the guy told me to check all GND and VCC connections. Turned out some via's to the ground plane were disconnected. Since the IC has lot's of GND and VCC connections, some of them internally connected you can't find this problem with just a continuity tester. With a good ohm-meter I've found about 0.05 ohm difference on these disconnected pins and after testing an unassembled PCB I found they were actually disconnected. This taught me not to assume anything is actually connected without testing it... (That board had a TTL crystal oscillator, these babies always work like a charm if you can afford the cost... +5V, GND and a really nice clock). When I soldered some wirewrap wires from these pins to GND it ran fine (But I had the wind knocked out of my sails...) Guy