Post by thread:[PIC]: My 16F877/20 enters in coma at 20 Mhz !!

Hi, PicDoctors, I am trying to work with a 16F877/20 at 20 MHz. I program it with the HS option bit set, and have tried different capacitor values : 27 pF and 47 pF. Nothing at all : I look with my scope in the OSCOUT pin and the encephalogram is flat. If I substitute the 20 MHz for a 4 Mhz one, my 16F877 comes to live again (even without changing the HS bit for the XT one). If I use the 4 Mhz quartz with the XT bit set, it is also OK. Please, PicDoctors, can some of you suggest how can I reanimate my 16F877 at 20 MHz ? Thanks ! -------------------------------------------------------------- Joan Ilari e-mail : spam_OUTjoanTakeThisOuTilari.org Barcelona www : http://www.ilari.org Spain Voice : +34 93 431 96 39 "I've seen things you people wouldn't believe. Attack ships on fire off the shoulder of Orion. I watched C-beams glitter in the dark near the Tannhauser gate. All those moments will be lost in time, like tears in rain. Time to die..." -Blade Runner- --------------------------------------------------------------- -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

Using ICD currently on a 16F876/20 . Using 15pF caps on a production board. Works perfectly. Just realised my OSCI setting is still set at XT . Forgot to change it to HS when I went from 4 Mhz prototype to 20 Mhz production. Then again, I also have not tested it without ICD. Maybe you should also check that your PIC is initialized properly. Quentin -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Try a 20MHz crystal specified for parallel operation. Most 20MHz crystals that are unspec'd are either series or 6.66 MHz 3rd overtone and will not move at 20MHz without a tank circuit in a normal 'gate' oscillator. Peter -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam.....mitvma.mit.edu

What have I to ask for when in my electronics shop : a parallel operation 20 Mhz crystal quartz ? What about the cutting type of crystal ? Is there any page where all this is explained ? Gracies ! Joan {Quote hidden}> -----Mensaje original----- > De: pic microcontroller discussion list > [EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU]En nombre de Peter L. Peres > Enviado el: sabado, 26 de mayo de 2001 10:07 > Para: PICLISTspam_OUTMITVMA.MIT.EDU > Asunto: [PIC]: My 16F877/20 enters in coma at 20 Mhz !! > > > Try a 20MHz crystal specified for parallel operation. Most 20MHz crystals > that are unspec'd are either series or 6.66 MHz 3rd overtone and will not > move at 20MHz without a tank circuit in a normal 'gate' oscillator. > > Peter > > -- > http://www.piclist.com hint: To leave the PICList > @spam@piclist-unsubscribe-requestKILLspammitvma.mit.edu > > -- http://www.piclist.com hint: To leave the PICList KILLspampiclist-unsubscribe-requestKILLspammitvma.mit.edu

> What have I to ask for when in my electronics shop : a parallel > operation 20 Mhz crystal quartz ? What about the cutting type of > crystal ? Is there any page where all this is explained ? > > Gracies ! > > Joan Joan, ask for a parallel operation 20MHz crystal for microprocessor use (probably 100 ppm tolerance). Ask for the recommended caps for it. Better sources will tell you this (like Mouser etc). Buy two identical crystals. If you ever have a doubt about having damaged one, swap them. If it's still the same problem it's very unlikely that it's the crystal. This also applies for other key parts in the circuit. good luck, Peter -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

At 09:07 PM 5/27/01 +0300, Peter L. Peres wrote: > > What have I to ask for when in my electronics shop : a parallel > > operation 20 Mhz crystal quartz ? What about the cutting type of > > crystal ? Is there any page where all this is explained ? > > > > Gracies ! > > > > Joan > >Joan, ask for a parallel operation 20MHz crystal for microprocessor use >(probably 100 ppm tolerance). Ask for the recommended caps for it. Beware. The loading capacitance value (typical 20pF) needs to be doubled, and then cut back a bit for typical apps. http://www.dvanhorn.org/Micros/All/Crystals.php has the details. -- Dave's Engineering Page: http://www.dvanhorn.org I would have a link to FINDU here in my signature line, but due to the inability of sysadmins at TELOCITY to differentiate a signature line from the text of an email, I am forbidden to have it. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> Beware. The loading capacitance value (typical 20pF) needs to be > doubled, and then cut back a bit for typical apps. > http://www.dvanhorn.org/Micros/All/Crystals.php has the details. Better sources tell you directly what caps to use (not the real load cap). So be sure NOT to double those. Double if they tell you 'load cap is X pF'. Do not double if they say 'use X pF capacitors'. Beware, Dave. ;-) Peter -- 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 09:05 AM 5/28/01 +0300, Peter L. Peres wrote: > > Beware. The loading capacitance value (typical 20pF) needs to be > > doubled, and then cut back a bit for typical apps. > > http://www.dvanhorn.org/Micros/All/Crystals.php has the details. > >Better sources tell you directly what caps to use (not the real load cap). >So be sure NOT to double those. Double if they tell you 'load cap >is X pF'. Do not double if they say 'use X pF capacitors'. Beware, Dave. >;-) How would they know what your parasitics are in your circuit? Granted, they can probably give you a value within 20% or so. -- Dave's Engineering Page: http://www.dvanhorn.org I would have a link to FINDU here in my signature line, but due to the inability of sysadmins at TELOCITY to differentiate a signature line from the text of an email, I am forbidden to have it. -- 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