Post by thread:[PIC:] Oscilator on Timer1 hangs up !!!!

Hello everyone, I4m using Timer1 with a 32,768Khz cristal for waking up an 16F628 every 15 seconds. Everything works fine, TILL CRISTAL STOPS OSCILLATING !!! I4ve put two 27pf caps to ground on each pin of cristal, but it ussually stops oscillating after a few minutes. If I put the scope probe on T1OSO or T1OSI, it starts oscillating again. For solving this problem, have put a 4,7Mohm R in parallel with cristal. Have changed it up to 10Mohm, but what only did, is change time till it stops running. Also changed cap values, used other cristals, and other 16F6284s !!!!!!!!!!! Does anyne know how should I fix this ?????? Thanks in advance, Gabriel.- -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

At 01:18 PM 1/8/2004 -0300, you wrote: >Hello everyone, > > I4m using Timer1 with a 32,768Khz cristal for waking up an >16F628 >every 15 seconds. Everything works fine, TILL CRISTAL STOPS OSCILLATING !!! > I4ve put two 27pf caps to ground on each pin of cristal, > but it ussually >stops >oscillating after a few minutes. If I put the scope probe on T1OSO or T1OSI, >it starts oscillating >again. > For solving this problem, have put a 4,7Mohm R in > parallel with cristal. >Have changed it up to 10Mohm, >but what only did, is change time till it stops running. > Also changed cap values, used other cristals, and other > 16F6284s >!!!!!!!!!!! Series resistor value? You'll likely overdrive and destroy the crystal without a fairly high value resistor. Too high and it won't start reliably. Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" spam_OUTspeffTakeThisOuTinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> two 27pf caps to ground on each pin of cristal > Also changed cap values, used other cristals, and other > 16F6284s !!!!!!!!!!! I always use 47pF. It's a little slow starting but it keeps going >, but it usually stops oscillating after a few minutes. If I put the > scope probe on T1OSO or T1OSI, it starts oscillating again Sounds like a physical fault. I'd check for a short and remove any flux that may be bridging tracks. How's the humidity where you are ? But you say you've changed the caps and crystal. Often that soldering/de-soldering would change or remove the fault Are the caps really grounded ? I would have suggested a weirdness in your s/w that turns TMR1 off or does something strange to RB6 / RB7. That doesn't explain why the turn-off time changes wrt a parallel resistor However, as you don't know the cause of the problem, you can't rule anything out, neither obvious nor obscure -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics