Post by thread:[PIC]: PIC crystal...

Maximum speed of the chip. Rick Shirollah Ghadirian wrote: {Quote hidden}> Hi all, > > When it says on the chip 04 or 08 for the speed of the chip, is it the > crystal value or 1/4 of the crystal value. > > Thanks in advance. > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

...and what can cause my PIC16F84A-20P to work with a 4MHz resonator but not a 20MHz resonator? I have tried two different 20 MHz resonators and the chip doesn't work with either... 4MHz is just fine. The application is a simple LED turn on and keep on, so speed should make no difference. Any ideas? - Programmed with MPLab and the properties for the project specify 20MHz. XT is specified as the type... I don't need the extra speed at the moment, but I am curious what I might be missing. My tools to track this problem are not advanced - no oscillator, etc... A logic probe is about all I have. Thank you, Fowler {Original Message removed}

Try a 1 to 10 meg resistor across the osc pins. I think I saw a datasheet somewhere with this requirement. Rick "Fowler, Paul B." wrote: {Quote hidden}> ...and what can cause my PIC16F84A-20P to work with a 4MHz resonator but not > a 20MHz resonator? > > I have tried two different 20 MHz resonators and the chip doesn't work with > either... 4MHz is just fine. The application is a simple LED turn on and > keep on, so speed should make no difference. > > Any ideas? - Programmed with MPLab and the properties for the project > specify 20MHz. XT is specified as the type... > > I don't need the extra speed at the moment, but I am curious what I might be > missing. My tools to track this problem are not advanced - no oscillator, > etc... A logic probe is about all I have. > > Thank you, > Fowler > > {Original Message removed}

At 11:05 PM 10/03/2002 -0500, you wrote: >...and what can cause my PIC16F84A-20P to work with a 4MHz resonator but not >a 20MHz resonator? > >I have tried two different 20 MHz resonators and the chip doesn't work with >either... 4MHz is just fine. The application is a simple LED turn on and >keep on, so speed should make no difference. > >Any ideas? - Programmed with MPLab and the properties for the project >specify 20MHz. XT is specified as the type... Change the oscillator type to HS for above 4MHz. Regards... -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

are you using a decoupling cap with the pic? ----- Original Message ----- From: Fowler, Paul B. <spam_OUTpaul.fowlerTakeThisOuTUNISYS.COM> To: <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> Sent: Sunday, March 10, 2002 8:05 PM Subject: Re: [PIC]: PIC crystal... > ...and what can cause my PIC16F84A-20P to work with a 4MHz resonator but not > a 20MHz resonator? > > I have tried two different 20 MHz resonators and the chip doesn't work with > either... 4MHz is just fine. The application is a simple LED turn on and > keep on, so speed should make no difference. > > Any ideas? - Programmed with MPLab and the properties for the project > specify 20MHz. XT is specified as the type... > > I don't need the extra speed at the moment, but I am curious what I might be > missing. My tools to track this problem are not advanced - no oscillator, > etc... A logic probe is about all I have. > > Thank you, > Fowler > > {Original Message removed}

Changing it to HS did the trick!!! It now runs at 20MHz. Thank you Piclist, Fowler -----Original Message----- From: David Duffy [piclistKILLspamAUDIOVISUALDEVICES.COM.AU] Sent: Sunday, March 10, 2002 11:21 PM To: .....PICLISTKILLspam.....MITVMA.MIT.EDU Subject: Re: [PIC]: PIC crystal... At 11:05 PM 10/03/2002 -0500, you wrote: >...and what can cause my PIC16F84A-20P to work with a 4MHz resonator but not >a 20MHz resonator? > >I have tried two different 20 MHz resonators and the chip doesn't work with >either... 4MHz is just fine. The application is a simple LED turn on and >keep on, so speed should make no difference. > >Any ideas? - Programmed with MPLab and the properties for the project >specify 20MHz. XT is specified as the type... Change the oscillator type to HS for above 4MHz. Regards... -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> When it says on the chip 04 or 08 for the speed of the chip, is it the > crystal value or 1/4 of the crystal value. The oscillator frequency, or 4x the instruction speed. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, EraseMEolinspam_OUTTakeThisOuTembedinc.com, http://www.embedinc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

> ...and what can cause my PIC16F84A-20P to work with a 4MHz resonator but not > a 20MHz resonator? XT instead of HS oscillator mode, for one. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, @spam@olinKILLspamembedinc.com, http://www.embedinc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

> Try a 1 to 10 meg resistor across the osc pins. I think I saw a datasheet > somewhere with this requirement. I haven't. Care to provide a reference? ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, RemoveMEolinTakeThisOuTembedinc.com, http://www.embedinc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body

I've run into this problem with a few of my chips. I suspect the major reason is the extra capacitance from the breadboards I use. One person I talked to awhile ago measured 20pF extra capacitance from wire to wire on their breadboard... (I doubt you'll ever find your breadboard that high, but they still have enough to mess with sensitive circuits) But I've never needed the extra speed badly enough to really look into it hard. Use a wire wrap socket for the pic, bend the osc pins out and up so they don't go into the breadboard, and solder the osc (or another socket) directly to those pins with a flying lead to ground (or to the capacitors). -Adam Fowler, Paul B. wrote: {Quote hidden}>...and what can cause my PIC16F84A-20P to work with a 4MHz resonator but not >a 20MHz resonator? > >I have tried two different 20 MHz resonators and the chip doesn't work with >either... 4MHz is just fine. The application is a simple LED turn on and >keep on, so speed should make no difference. > >Any ideas? - Programmed with MPLab and the properties for the project >specify 20MHz. XT is specified as the type... > >I don't need the extra speed at the moment, but I am curious what I might be >missing. My tools to track this problem are not advanced - no oscillator, >etc... A logic probe is about all I have. > >Thank you, >Fowler > >{Original Message removed}

> When it says on the chip 04 or 08 for the speed of the chip, is it the > crystal value or 1/4 of the crystal value. It is the crystal value. The actual instruction rate is 1/4 this (except for branches). TTYL -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email TakeThisOuTlistservEraseMEspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

> ...and what can cause my PIC16F84A-20P to work with a 4MHz > resonator but not > a 20MHz resonator? > > I have tried two different 20 MHz resonators and the chip doesn't > work with > either... 4MHz is just fine. The application is a simple LED turn on and > keep on, so speed should make no difference. > > Any ideas? - Programmed with MPLab and the properties for the project > specify 20MHz. XT is specified as the type... > > I don't need the extra speed at the moment, but I am curious what > I might be > missing. My tools to track this problem are not advanced - no oscillator, > etc... A logic probe is about all I have. A resonator (those 4 pin beauties) or a crystal? I only ask since it a prior message you said crystal. For a crystal you must use HS mode to get it to work since the crystal must be driven a little "harder". For a resonator I'm not sure, I think XT should work? TTYL -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

Herbert wrote: > > ...and what can cause my PIC16F84A-20P to work with a 4MHz > > resonator but not > > a 20MHz resonator? <snip> >A resonator (those 4 pin beauties) or a crystal? I only ask since it a >prior message you said crystal. For a crystal you must use HS mode to get it >to work since the crystal must be driven a little "harder". For a resonator >I'm not sure, I think XT should work? TTYL No, HS is required for a 20MHz resonator. Been there, forgot that ! Regards... -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservEraseME.....mitvma.mit.edu with SET PICList DIGEST in the body

You haven't looked hard enough. Just about every CMOS clock circuit I've seen has a feedback resistor across its input/output typically 1 meg to 10 meg. This ensures a reliable startup. The PIC16f is a CMOS device with a high input impedance pin and a low output impedance pin (typical of CMOS clock generators). The data sheet for the 75T202 chip recommends a 10 meg resistor. The Basic Micro http://www.basicmicro.com/ MBasic manual page 146 recommends a 10 meg resistor across the 16f628 using a resonator. The Motorola CMOS handbook is infested with clock circuits with this feedback resistor. I have designed equipment with CMOS logic in commercial/broadcast circuits that use this resistor. VDO specifies this resistor in their automotive applications in their instrument clusters. The Piccon at http://www.qsl.net/n6bg/piccon/ shows a 1 meg across the xtal. The Simon Bus radio alert receiver uses a PIC, 4mhz xtal with a 10 meg across its clock. I could go on and on..... Rick Olin Lathrop wrote: {Quote hidden}> > Try a 1 to 10 meg resistor across the osc pins. I think I saw a datasheet > > somewhere with this requirement. > > I haven't. Care to provide a reference? > > ******************************************************************** > Olin Lathrop, embedded systems consultant in Littleton Massachusetts > (978) 742-9014, EraseMEolinembedinc.com, http://www.embedinc.com > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email RemoveMElistservEraseMEEraseMEmitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservspam_OUTKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Rick wrote: >You haven't looked hard enough. Just about every CMOS clock circuit I've seen >has a feedback resistor across its input/output typically 1 meg to 10 meg. >This >ensures a reliable startup. The PIC16f is a CMOS device with a high input >impedance pin and a low output impedance pin (typical of CMOS clock >generators). The data sheet for the 75T202 chip recommends a 10 meg resistor. What Olin is saying is that Microchip don't mention it do they? I would not say a 16F628 oscillator is the same as a standard CMOS clock circuit. {Quote hidden}>The Basic Micro http://www.basicmicro.com/ MBasic manual page 146 >recommends a >10 meg resistor across the 16f628 using a resonator. The Motorola CMOS >handbook >is infested with clock circuits with this feedback resistor. I have designed >equipment with CMOS logic in commercial/broadcast circuits that use this >resistor. VDO specifies this resistor in their automotive applications in >their >instrument clusters. The Piccon at http://www.qsl.net/n6bg/piccon/ shows a 1 >meg across the xtal. The Simon Bus radio alert receiver uses a PIC, 4mhz xtal >with a 10 meg across its clock. I could go on and on..... >Rick Are any of these examples what Microchip suggest? I'd say some designers add the resistor out of habit with other micro's. >Olin Lathrop wrote: > > > > Try a 1 to 10 meg resistor across the osc pins. I think I saw a datasheet > > > somewhere with this requirement. > > > > I haven't. Care to provide a reference? -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTspammitvma.mit.edu with SET PICList DIGEST in the body

> What Olin is saying is that Microchip don't mention it do they? > I would not say a 16F628 oscillator is the same as a standard > CMOS clock circuit. Figure 14.2 of the 16F628 manual shows a resistor "RF" inside the chip, across Osc1 and Osc2. Unfortunately nothing else is said about it -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspamspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body

> You haven't looked hard enough. Just about every CMOS clock circuit I've seen > has a feedback resistor across its input/output typically 1 meg to 10 meg. This > ensures a reliable startup. The PIC16f is a CMOS device with a high input > impedance pin and a low output impedance pin (typical of CMOS clock > generators). The data sheet for the 75T202 chip recommends a 10 meg resistor. > The Basic Micro http://www.basicmicro.com/ MBasic manual page 146 recommends a > 10 meg resistor across the 16f628 using a resonator. The Motorola CMOS handbook > is infested with clock circuits with this feedback resistor. I have designed > equipment with CMOS logic in commercial/broadcast circuits that use this > resistor. VDO specifies this resistor in their automotive applications in their > instrument clusters. The Piccon at http://www.qsl.net/n6bg/piccon/ shows a 1 > meg across the xtal. The Simon Bus radio alert receiver uses a PIC, 4mhz xtal > with a 10 meg across its clock. I could go on and on..... But not one of these references are from Microchip specifically pertaining to the PIC crystal driver circuit, which was topic of discussion. Such resistors are often used as negative feedback to keep CMOS logic gates in the "linear" region. However, the PIC oscillator circuit was designed specifically for that purpose and needs no such resistor. Adding such a resistor to the PIC crystal oscillator is merely superstition. You might just as well wave a dead fish over it during a full moon. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, RemoveMEolinKILLspamembedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestSTOPspamspam_OUTmitvma.mit.edu

Ahh, the technique which gets used to make the ICD work properly.... > Such resistors are often used as negative feedback to keep > CMOS logic gates in the "linear" region. However, the PIC > oscillator circuit was designed specifically for that purpose > and needs no such resistor. Adding such a resistor to the > PIC crystal oscillator is merely superstition. You might > just as well wave a dead fish over it during a full moon. > > > ******************************************************************** > Olin Lathrop, embedded systems consultant in Littleton Massachusetts > (978) 742-9014, spamBeGoneolinSTOPspamEraseMEembedinc.com, http://www.embedinc.com > > -- > http://www.piclist.com hint: To leave the PICList KILLspampiclist-unsubscribe-requestspamBeGonemitvma.mit.edu ***************************************************************** This email has been checked by the altohiway e-Sweeper Service ***************************************************************** -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestEraseMEmitvma.mit.edu

Actually the salts in the fish flesh cause ionic reactions which in turn generate electrostatic fields that, while the fish is moving, interact with the earth's magnetic field which, of course, is affected by the full moon thus causing ionic bombardment of the silicon substrate. Thus waving a dead fish over your PIC during a full moon CAN have an electrical effect on it. If you've read thus far... only joking! ;-) Ted Mawson PS We engineering types do have a tendancy to reject anything that we don't have a scientific explanation for, don't you think? {Original Message removed}

At 08:14 AM 3/12/02 -0500, you wrote: >Such resistors are often used as negative feedback to keep CMOS logic gates >in the "linear" region. However, the PIC oscillator circuit was designed >specifically for that purpose and needs no such resistor. Actually all circuits of this type (Pierce oscillator) do require a resistor, however the resistor is provided internally in PICs. The value is selected from several possibilities when the oscillator type is selected. Some micros (Motorola '05, for example) do not have the resistor internally and it must be provided externally. This might have some slight advantage in allowing better controlled value (5% vs. 30% tolerance) and higher value (10M vs maybe 2M). > Adding such a >resistor to the PIC crystal oscillator is merely superstition. You might >just as well wave a dead fish over it during a full moon. Like waving a fish over it twice, when once has been show beyond any doubt to be every bit as effective as twice. Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" spamBeGonespeffKILLspaminterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com 9/11 United we Stand -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestspam_OUTmitvma.mit.edu

No, but it works better when the fish is alive. http://whozoo.org/Intro2000/tashcorm/tempagetwo.htm Unfortunately, they didn't include a full datasheet so I have to guess how to use it in a circuit. Karl Quoting Dale Botkin <TakeThisOuTdale.....TakeThisOuTBOTKIN.ORG>: {Quote hidden}> On Tue, 12 Mar 2002, Olin Lathrop wrote: > > > You might just as well wave a dead fish over it during a full moon. > > What - am I the only one that does that?? > > Dale > 8-) > > -- > http://www.piclist.com hint: To leave the PICList > TakeThisOuTpiclist-unsubscribe-requestKILLspamspammitvma.mit.edu > > > -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestRemoveMEmitvma.mit.edu