Post by thread:[PIC] Help troubleshooting a F84 cct with dmm

>>> "Des Bromilow" <spam_OUTDes.BromilowTakeThisOuTcitec.com.au> 11/03/03 8:48:14 pm >>> G'Day, My circuit with a 16F84a operating off a 4MHz crystal (with 2 x 33pF caps) doesn't seem to work on the most simple of programming tests. I suspect my Crystal may be dead.. but I don't have a CRO to check, all I have to test with is a Digital multimeter (DMM) I would expect to see a 2.5 VDC voltage on OSC1, OSC2 due to the 5VDC clock, and it's duty cycle. IS that correct? (that an operating Crystal will appear to a DMM as 2.5 VDC?) Any assistance in this arena appreciated, Des Bromilow Brisbane OZ -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Thanks!!!, That's what I'm trying to do, but the LED code isn't even lighting up, hence why I suspected the clock. I'll desolder the Crystal and try another. Any tips for soldering Crystals? Des >>> EraseMEjoecolquittspam_OUTTakeThisOuTCLEAR.NET.NZ 12/03/03 6:40:07 am >>> A DMM will likely collapse the oscillator and you'll read nothing. Even a x1 scope probe can do that. IMHO your best bet is parts substitution, a thorough circuit check and a little LED code -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

If possible, try and obtain a 16f628 - they are cheaper than the f84 and offer more features... one important one pertaining to your application: The internal 4MHz oscillator. You will save yourself a lot of time and trouble by switching to this chip. That is, of course, if it is a viable option. Quoting Jinx <KILLspamjoecolquittKILLspamCLEAR.NET.NZ>: {Quote hidden}> A DMM will likely collapse the oscillator and you'll read > nothing. Even a x1 scope probe can do that. IMHO your > best bet is parts substitution, a thorough circuit check and > a little LED code > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body > ---------------------------------------- This mail sent through http://www.mywaterloo.ca -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body

> Any tips for soldering Crystals? Don't dither (ie don't overheat), and ground the case. Mount xtal and caps as close as possible to the PIC and add a couple of decoupling caps, something like a 10uF+10n, also as close as possible to the PIC Osc problems do happen so you could be right. I'd still be tempted to do a methodical pin-by-pin circuit check. How often do "obvious" errors magically appear ? 8-) -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email TakeThisOuTlistservEraseMEspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

At 06:10 AM 3/12/03 +1000, Des Bromilow wrote: > >>> "Des Bromilow" <RemoveMEDes.BromilowTakeThisOuTcitec.com.au> 11/03/03 8:48:14 pm >>> >G'Day, >My circuit with a 16F84a operating off a 4MHz crystal (with 2 x 33pF caps) >doesn't seem to work on the most simple of programming tests. >I suspect my Crystal may be dead.. but I don't have a CRO to check, all I >have to test with is a Digital multimeter (DMM) >I would expect to see a 2.5 VDC voltage on OSC1, OSC2 due to the 5VDC >clock, and it's duty cycle. You can check the OSC2 pin with a multi-meter if you wrap one end of a 100K resistor on the positive test lead and use the free end of the resistor to measure the DC voltage. It should be about 1/2 the supply voltage. The 100K resistor isolates the capacitance of the DMM and test leads from the crystal and allows it to continue oscillating (if it is). This same trick does not work on the OSC1 pin - even 100K load is usually too much. If it looks like an oscillator problem, try removing the crystal components and configuring the PIC to use external RC oscillator mode. This requires connecting a resistor from Vdd to OSC1 and a small capacitor from OSC1 to ground. See the data sheet for the details. The accuracy is horrific but you can at least get a LED flashing. Then work back to using the crystal. One final thought - just for the heck of it, try changing from XT mode to HS mode before giving up on your current crystal configuration. dwayne -- Dwayne Reid <dwaynerEraseME.....planet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 19 years of Engineering Innovation (1984 - 2003) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservmitvma.mit.edu with SET PICList DIGEST in the body

Thanks!!! FWIW, I am using it in HS mode.. that is correct isn't it? or should I be in XT mode? Thanks, Des >>> RemoveMEdwaynerEraseMEEraseMEPLANET.EON.NET 12/03/03 7:07:31 am >>> At 06:10 AM 3/12/03 +1000, Des Bromilow wrote: > >>> "Des Bromilow" <RemoveMEDes.Bromilowspam_OUTKILLspamcitec.com.au> 11/03/03 8:48:14 pm >>> >G'Day, >My circuit with a 16F84a operating off a 4MHz crystal (with 2 x 33pF caps) >doesn't seem to work on the most simple of programming tests. >I suspect my Crystal may be dead.. but I don't have a CRO to check, all I >have to test with is a Digital multimeter (DMM) >I would expect to see a 2.5 VDC voltage on OSC1, OSC2 due to the 5VDC >clock, and it's duty cycle. You can check the OSC2 pin with a multi-meter if you wrap one end of a 100K resistor on the positive test lead and use the free end of the resistor to measure the DC voltage. It should be about 1/2 the supply voltage. The 100K resistor isolates the capacitance of the DMM and test leads from the crystal and allows it to continue oscillating (if it is). This same trick does not work on the OSC1 pin - even 100K load is usually too much. If it looks like an oscillator problem, try removing the crystal components and configuring the PIC to use external RC oscillator mode. This requires connecting a resistor from Vdd to OSC1 and a small capacitor from OSC1 to ground. See the data sheet for the details. The accuracy is horrific but you can at least get a LED flashing. Then work back to using the crystal. One final thought - just for the heck of it, try changing from XT mode to HS mode before giving up on your current crystal configuration. dwayne -- Dwayne Reid <RemoveMEdwaynerTakeThisOuTspamplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 19 years of Engineering Innovation (1984 - 2003) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspamspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

> FWIW, I am using it in HS mode.. that is correct isn't it? or > should I be in XT mode? It SHOULD be XT for a 4MHz crystal, I'm not sure what would happen in HS mode, you might damage the crystal, or result in no oscillation. I'm not familiar enough to know, it's possible it would just work, with higher power consumption. Please though, READ THE DATASHEET, this is VERY CLEAR in the datasheet and if you haven't perused the datasheet properly you are wasting our time. Sorry to be so harsh, but a PIC is something you NEED to consult the datasheet for. I've been working with PICs on a hobby level for a few years and STILL have to regularly consult the datasheet. TTYL -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservSTOPspamspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

Thanks!!.. I was under the inpression that the XT setting was for crystals lower than 4MHz, and HS for the higher than 4MHz...Goes to show I obviously didn't read far enough into it to pick the difference. Thanks, again, Des >>> spamBeGonemailinglistSTOPspamEraseMEFARCITE.NET 12/03/03 8:10:36 am >>> > FWIW, I am using it in HS mode.. that is correct isn't it? or > should I be in XT mode? It SHOULD be XT for a 4MHz crystal, I'm not sure what would happen in HS mode, you might damage the crystal, or result in no oscillation. I'm not familiar enough to know, it's possible it would just work, with higher power consumption. Please though, READ THE DATASHEET, this is VERY CLEAR in the datasheet and if you haven't perused the datasheet properly you are wasting our time. Sorry to be so harsh, but a PIC is something you NEED to consult the datasheet for. I've been working with PICs on a hobby level for a few years and STILL have to regularly consult the datasheet. TTYL -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservEraseMEmitvma.mit.edu with SET PICList DIGEST in the body

{Quote hidden}> -----Original Message----- > From: Herbert Graf [SMTP:@spam@mailinglist@spam@spam_OUTFARCITE.NET] > Sent: Tuesday, March 11, 2003 10:11 PM > To: spamBeGonePICLISTKILLspamMITVMA.MIT.EDU > Subject: Re: [PIC] Help troubleshooting a F84 cct with dmm > > > FWIW, I am using it in HS mode.. that is correct isn't it? or > > should I be in XT mode? > > It SHOULD be XT for a 4MHz crystal, I'm not sure what would happen > in HS > mode, you might damage the crystal, or result in no oscillation. I'm not > familiar enough to know, it's possible it would just work, with higher > power > consumption. > Please though, READ THE DATASHEET, this is VERY CLEAR in the > datasheet and > if you haven't perused the datasheet properly you are wasting our time. > Sorry to be so harsh, but a PIC is something you NEED to consult the > datasheet for. I've been working with PICs on a hobby level for a few > years > and STILL have to regularly consult the datasheet. TTYL > It will almost certainly still work with the HS setting. Long term reliability may be slightly compromised, and the oscillator may not be exactly on frequency if it is being overdriven. FWIW I've had to use the HS setting when using certain 4MHz ceramic resonators with built in caps that simply wouldn't start reliably using the XT fuse setting. Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. ======================================================================= Any questions about Bookham's E-Mail service should be directed to .....postmasterspam_OUTbookham.com. -- http://www.piclist.com hint: To leave the PICList TakeThisOuTpiclist-unsubscribe-request.....TakeThisOuTmitvma.mit.edu>