Post by thread:Pic Osc Problems

HI All Has anyone else had problems with pics and oscillators? we can not get the levels on the OSC1 and OSC2 pins to a sufficently good level the mchip data book says 0.7xVDD however getting this takes a large ammount of time and playing arround. We found that for a 71/54C @500k the best values were 150p(osc2) and 100p(osc1) but then the load capacitance is unmatched and the waveform on osc1 is distorted. Has anyone done any work on getting the best out of resonators(murata are the ones we use). We use 500k 2M and 4M, with each increase in value it is becoming harder to get 0.7VDD any ideas/ recomendations. Sory to go on about it but anyone seen the ATMEL AVR simulator yet... they put in a command line like the old MPSIM for DOS, Horray :-) Robert Drake - Development Engineer EMS

On Wed, 9 Jul 1997 08:05:28 +0100 Robert Drake <spam_OUTrobertTakeThisOuTEMS1.DEMON.CO.UK> writes: >HI All > Has anyone else had problems with pics and oscillators? we can >not get the levels on the OSC1 and OSC2 pins to a sufficently good >level >the mchip data book says 0.7xVDD however getting this takes a large >ammount of time and playing arround. We found that for a 71/54C @500k >the best values were 150p(osc2) and 100p(osc1) but then the load >capacitance is unmatched and the waveform on osc1 is distorted. Has >anyone done any work on getting the best out of resonators(murata are >the ones we use). We use 500k 2M and 4M, with each increase in value >it >is becoming harder to get 0.7VDD any ideas/ recomendations. We are using muRata resonators with built-in capacitors at 16 MHz. They have worked well for us. We originally tried some from ECS and from Integrity Technology. Both worked well in the prototypes but failed in production. We were getting about a 50% failure rate. We have not had any of the muRata's not work. We talked with ECS, Integrity and muRata. Also talked with Microchip about getting a good model of the oscillator (on the 16C74A) (graphs of input Z, output Z, gain and phase vs frequency) so we could pass that on to the resonator companies. Microchip did not have that info available. They pointed out that their oscillator documentation isn't worse than anyone else's (true...). murata said they were working with Microchip in Japan to characterize resonators for use with the mMicrochip chips. For now, we're using muRata with built in capacitors! Harold

we tend to use 4meg ceramics a lot and tho' we get them from various suppliers, find about 10 per cent or so won't work. (on any pic) {Quote hidden}> Has anyone else had problems with pics and oscillators? we can >not get the levels on the OSC1 and OSC2 pins to a sufficently good level >the mchip data book says 0.7xVDD however getting this takes a large >ammount of time and playing arround. We found that for a 71/54C @500k >the best values were 150p(osc2) and 100p(osc1) but then the load >capacitance is unmatched and the waveform on osc1 is distorted. Has >anyone done any work on getting the best out of resonators(murata are >the ones we use). We use 500k 2M and 4M, with each increase in value it >is becoming harder to get 0.7VDD any ideas/ recomendations. > Sory to go on about it but anyone seen the ATMEL AVR simulator >yet... they put in a command line like the old MPSIM for DOS, Horray :-) > > Robert Drake - Development Engineer EMS