Post by thread:[PIC]: Crystal recommendation?

I am using Digikey part number 300-6042-ND 20MHz crystal with 16F876, no problems. This is in an HC49/US case (does US standard for ultrashort?), a nice small package. US$0.88 each I am using them with 3x 39pF caps (but I didn't really check to see if that was right). The signal looks like a nice clean 5V sine on my scope. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

----- Original Message ----- From: Bob Ammerman <RAMMERMANKILLspamPRODIGY.NET> To: <.....PICLISTKILLspam.....MITVMA.MIT.EDU> Sent: Wednesday, December 06, 2000 6:05 PM Subject: Re: [PIC]: Crystal recommendation? > I am using Digikey part number 300-6042-ND 20MHz crystal with 16F876, no > problems. This is in an HC49/US case (does US standard for ultrashort?), a > nice small package. > > US$0.88 each > > I am using them with 3x 39pF caps (but I didn't really check to see if that > was right). The signal looks like a nice clean 5V sine on my scope. er... I mean 2x 39pF caps (now where would I put that third cap?) {Quote hidden}> Bob Ammerman > RAm Systems > (contract development of high performance, high function, low-level > software) > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

Dave Bell wrote: > Looking for a reference for 20 MHz crystal for a 16F(873/877)-20. > I assume it will be in HS mode, and need (TBD pF) parallel caps? > Something easy to locate would be nice! :{) Digikey, say? > > Dave > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body I have to say you are probably better served buying the complete oscillator from Digi-key. I just got 10 of them (20 Mhz.) at $2.50 each. No muss, no fuss, they just work. Small package, (4 pins in an 8 pin dip), and low power. -- * | __O Thomas C. Sefranek KILLspamtcsKILLspamcmcorp.com |_-\<,_ Amateur Radio Operator: WA1RHP (*)/ (*) Bicycle mobile on 145.41, 448.625 MHz ARRL Instructor, Technical Specialist, VE Contact. hamradio.cmcorp.com/inventory/Inventory.html http://www.harvardrepeater.org -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

> I have to say you are probably better served buying the complete > oscillator from Digi-key. > I just got 10 of them (20 Mhz.) at $2.50 each. No muss, no fuss, they > just work. > Small package, (4 pins in an 8 pin dip), and low power. That can be a convenience for a low volume product, but will cost at least double what the crystal and two caps cost. One good reason for having an external oscillator is if you are driving multiple devices from the same clock. I've never had any problem with having the PIC drive a crystal directly (except the time I didn't cover the window on a 16C77/JW), and I think of this as the "easy" solution. ***************************************************************** Olin Lathrop, embedded systems consultant in Devens Massachusetts (978) 772-3129, spamBeGoneolinspamBeGoneembedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: To leave the PICList TakeThisOuTpiclist-unsubscribe-requestEraseMEspam_OUTmitvma.mit.edu

I agree that the crystal and two 33 pf caps usually works very well at 20MHz. The only trick to remember in troubleshooting is that when you probe with the oscilloscope probe, use the X10 (times 10) impedance instead of the X1. Using the X1 setting will stop the oscillation when the scope probe makes contact. This gives the impression that the crystal is bad when it is not. -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

One of the ways we made things adjustable with RF equipment we were working on was to connect OSC1 to a logic gate (inverter), and subtract it's input capacitance from the cap that's normally there. You can then attach a probe to the output of the logic gate, which is now isolated quite well from the oscillations of the micro. Now that Fairchild et al have single logic gates available in SOT-23 form, it is very easy to justify the addition of the pads for the gate. C1 = C2 - C of logic gate If you need to tune the frequency, make the one cap a varcap o-----|>o--- Test Point | o--------------------OSC1 | o-----|X|------o-----OSC2 | | | | - C1 C2- - _ | | | | GND GND Fred Bailey <baile_fEraseME.....TDIPOWER.COM> on 12/07/2000 09:10:26 AM Please respond to pic microcontroller discussion list <EraseMEPICLISTMITVMA.MIT.EDU> To: RemoveMEPICLISTEraseMEEraseMEMITVMA.MIT.EDU cc: (bcc: Andrew Kunz/TDI_NOTES) Subject: Re: [PIC]: Crystal recommendation? I agree that the crystal and two 33 pf caps usually works very well at 20MHz. The only trick to remember in troubleshooting is that when you probe with the oscilloscope probe, use the X10 (times 10) impedance instead of the X1. Using the X1 setting will stop the oscillation when the scope probe makes contact. This gives the impression that the crystal is bad when it is not. -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestspam_OUTKILLspammitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestTakeThisOuTspammitvma.mit.edu

At 09:10 AM 12/7/00 -0500, you wrote: >I agree that the crystal and two 33 pf caps usually works very well at 20MHz. >The only trick to remember in troubleshooting is that when you probe with the >oscilloscope probe, use the X10 (times 10) impedance instead of the X1. Using >the X1 setting will stop the oscillation when the scope probe makes contact. >This gives the impression that the crystal is bad when it is not. Probe the crystal case. This will not give full output voltage, but it will also not stop the osc, and will barely affect frequency. Otherwise, the handy shortwave radio works really well. -- Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspamspamBeGonemitvma.mit.edu

On Thu, 7 Dec 2000 08:34:48 -0500 Olin Lathrop <RemoveMEolin_piclistKILLspamEMBEDINC.COM> writes: {Quote hidden}> > I have to say you are probably better served buying the complete > > oscillator from Digi-key. > > I just got 10 of them (20 Mhz.) at $2.50 each. No muss, no fuss, > they > > just work. > > Small package, (4 pins in an 8 pin dip), and low power. > > That can be a convenience for a low volume product, but will cost at > least > double what the crystal and two caps cost. One good reason for > having an > external oscillator is if you are driving multiple devices from the > same > clock. > > I've never had any problem with having the PIC drive a crystal > directly > (except the time I didn't cover the window on a 16C77/JW), and I > think of > this as the "easy" solution. > And we're getting ceramic resonators with built-in capacitors for something like 50 cents each. The cost savings over an external oscillator or even over a crystal and a couple capacitors is substantial. Also, there's a substantial savings in board space since the resonator with capacitors is in a 3 pin SIP (or even smaller when surface mounted). muRata has a nice search engine where you can put in a processor number and it will come back with resonator part numbers that have been characterised for that processor. It's at http://www.murata.co.jp/search/ic-e.html . Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/tagj. -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestSTOPspamspam_OUTmitvma.mit.edu

I've generally been able to probe the output side of the PIC oscillator with a 10x scope probe with no problem. Probing the input side kills it right away. When I'm doing "crash and burn" debugging for a chip for which I have no emulator, this is generally the first thing I check on the dead prototype. It obviously won't do anything without a live oscillator! In a previous post I mentioned how great ceramic resonators are. We've replaced crystals completely with resonators. I'm now working on a very small product that is all SMT using the PIC 16F627 running at 4 MHz. I'd generally found that at 4 MHz, pretty much anybody's resonator with caps would work. At 16 MHz, only the muRata would work reliably. On this latest project, I tried the only SMT resonator Digikey had (Panasonic, I think). It would not reliably work with the 16F627, so now I'm "surface mounting" a SIP resonator from them. Harold On Thu, 7 Dec 2000 11:34:26 -0500 David VanHorn <spamBeGonedvanhornSTOPspamEraseMECEDAR.NET> writes: {Quote hidden}> At 09:10 AM 12/7/00 -0500, you wrote: > >I agree that the crystal and two 33 pf caps usually works very well > at 20MHz. > >The only trick to remember in troubleshooting is that when you > probe with the > >oscilloscope probe, use the X10 (times 10) impedance instead of the > X1. Using > >the X1 setting will stop the oscillation when the scope probe makes > contact. > >This gives the impression that the crystal is bad when it is not. > > > Probe the crystal case. > This will not give full output voltage, but it will also not stop > the osc, > and will barely affect frequency. > > Otherwise, the handy shortwave radio works really well. > > -- > Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 > > -- > http://www.piclist.com hint: To leave the PICList > KILLspampiclist-unsubscribe-requestspamBeGonemitvma.mit.edu > > FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/tagj. -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestEraseMEmitvma.mit.edu

assuming you don't need the extreme accuracy of a crystal then I would have to agree with harold and go for a surface mount ceramic resonator with built in capacitors from murata . i have a load different boards with the 20MHz part fitted and they all work fine. one nice thing about resonators that's worth remembering is that they start up about 10 times faster than a crystal. not a great help for pic circuits as they have a start up delay anyway, but can be useful elsewhere. small, cheap and they also look cool... oh dear, time to get a life. regards, Simon -- http://www.piclist.com hint: To leave the PICList @spam@piclist-unsubscribe-request@spam@spam_OUTmitvma.mit.edu

> one nice thing about resonators that's worth remembering is that they start up about 10 times faster > than a crystal. not a great help for pic circuits as they have a start up delay anyway, but can be > useful elsewhere. I seem to remember reading in one of the PIC datasheets that you can turn the startup delay off. What exactly happens when it's off, but your clock isn't ready for prime time yet? Could you just put in a dozen or so nop instructions right after the wakeup to compensate? Or do "bad things" happen with a whacky clock? -Steve -- http://www.piclist.com hint: To leave the PICList spamBeGonepiclist-unsubscribe-requestKILLspammitvma.mit.edu

> I seem to remember reading in one of the PIC datasheets that you can turn > the startup delay off. I didn't look this up explicitly just now, but I remember there are two separate startup delays. There is a delay from the time Vcc gets above a threshold, which can be at least partially disabled on some PICs. For crystal oscillator mode (which also applies to ceramic resonators), there is an additional 1024 cycle delay to make sure the oscillator has stabalized. I don't think this delay can be disabled. ***************************************************************** Olin Lathrop, embedded systems consultant in Devens Massachusetts (978) 772-3129, .....olinspam_OUTembedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: To leave the PICList TakeThisOuTpiclist-unsubscribe-request.....TakeThisOuTmitvma.mit.edu