Post by thread:[PICLIST] [PIC] PIC16F84A

The manual for the PIC16F84 shows crystal for up to 10MHZ If I want to use higher crystals 19.6608MHz, can anybody recommend the capacitors to put in for the oscillators ? Is there any special circuit required ? Any help will be appreciated Derek -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

At 08:45 PM 1/9/2002 +0800, Derek Chan wrote: >The manual for the PIC16F84 shows crystal for up to 10MHZ > >If I want to use higher crystals 19.6608MHz, can anybody recommend the >capacitors to put in for the oscillators ? Is there any special circuit >required ? Any help will be appreciated The crystal determines the capacitors. Get the data sheet on the crystal. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On 09-Jan-02 dave vanhorn wrote: > At 08:45 PM 1/9/2002 +0800, Derek Chan wrote: >>The manual for the PIC16F84 shows crystal for up to 10MHZ >> >>If I want to use higher crystals 19.6608MHz, can anybody recommend the >>capacitors to put in for the oscillators ? Is there any special circuit >>required ? Any help will be appreciated > > The crystal determines the capacitors. > Get the data sheet on the crystal. I didn't think you could get 20Mhz 16F84s ?? Peter. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On Wed, Jan 09, 2002 at 02:05:06PM -0000, Peter Onion wrote: > On 09-Jan-02 dave vanhorn wrote: > > At 08:45 PM 1/9/2002 +0800, Derek Chan wrote: > >>The manual for the PIC16F84 shows crystal for up to 10MHZ > >> > >>If I want to use higher crystals 19.6608MHz, can anybody recommend the > >>capacitors to put in for the oscillators ? Is there any special circuit > >>required ? Any help will be appreciated > > > > The crystal determines the capacitors. > > Get the data sheet on the crystal. > > I didn't think you could get 20Mhz 16F84s ?? Reread the subject. He's talking about a 16F84A, which does go up to 20Mhz. And he has a valid question because the 16F84A manual only goes up to 10 Mhz even though the part can do 20. My answer is that the cap values are not as critical as you think. 15-30pF have worked fine with all the PIC based 20 Mhz crystal projects that I've done. This is a small detail that doesn't need to be sweated. BAJ -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

At 02:05 PM 1/9/2002 +0000, Peter Onion wrote: >On 09-Jan-02 dave vanhorn wrote: > > At 08:45 PM 1/9/2002 +0800, Derek Chan wrote: > >>The manual for the PIC16F84 shows crystal for up to 10MHZ > >> > >>If I want to use higher crystals 19.6608MHz, can anybody recommend the > >>capacitors to put in for the oscillators ? Is there any special circuit > >>required ? Any help will be appreciated > > > > The crystal determines the capacitors. > > Get the data sheet on the crystal. > >I didn't think you could get 20Mhz 16F84s ?? That's a different problem. (and potential flame-fest) -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On 09-Jan-02 Byron A Jeff wrote: > Reread the subject. He's talking about a 16F84A, which does go up to 20Mhz. Well in my defence I would quote this from the original post.... "The manual for the PIC16F84 shows crystal for up to 10MHZ" so I assumed that was the part he was using (since he had actually got the manual for it) rather than the "A" mentioned in the subject line :-) The 84 to 84A migration note is also rather unhelpful in that it just says "you'll have to try it and adjust the capacitor if it doesn't work right" > My answer is that the cap values are not as critical as you think. 15-30pF > have worked fine with all the PIC based 20 Mhz crystal projects that I've > done. I would imagine the oscilator circuit in the 84A is similar to the one used in other newer 20Mhz parts (eg 16F627) so as your experience shows 15-30pF would seem correct. Peter. ---------------------------------- E-Mail: Peter Onion <spam_OUTponionTakeThisOuTsrd.bt.co.uk> Date: 09-Jan-02 Time: 15:02:38 This message was sent by XFMail ---------------------------------- -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> >My answer is that the cap values are not as critical as you think. 15-30pF >have worked fine with all the PIC based 20 Mhz crystal projects that I've >done. > >This is a small detail that doesn't need to be sweated. True, if you really don't care wether you are on-frequency, or if your oscillator will 100% reliably start. Otherwise, you need to check these things. There's also a drive level spec, which should be checked. You need to measure the voltage while running, and get the impedance on resonance either from the DS or direct measurement (touchy). Overdriving crystals leads to failures and can shatter the 32kHz fork types. But, for the average hobbyist, the rule of thumb seems to be "ignore the specs, just guess". -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Hi, There are various speed for 16f84a. earlier ones operate at 4MHz, some operate at 10MHz and others operate at 20MHz. So if you have 20MHz 16f84a, why not! for example 16f84a-4I/P mean operate at the maximum speed of 4MHz. 16f84a-10I/P mean operate at the maximum speed of 10MHz. 16f84a-20I/P ==> 20MHz The figure in front of I determines the maximum speed that the controller can operate. good luck... Rgds, T.N.K --- dave vanhorn <.....dvanhornKILLspam@spam@CEDAR.NET> wrote: {Quote hidden}> At 08:45 PM 1/9/2002 +0800, Derek Chan wrote: > >The manual for the PIC16F84 shows crystal for up to > 10MHZ > > > >If I want to use higher crystals 19.6608MHz, can > anybody recommend the > >capacitors to put in for the oscillators ? Is there > any special circuit > >required ? Any help will be appreciated > > The crystal determines the capacitors. > Get the data sheet on the crystal. > > -- > http://www.piclist.com hint: The PICList is archived > three different > ways. See http://www.piclist.com/#archives for > details. > > __________________________________________________ Do You Yahoo!? Send FREE video emails in Yahoo! Mail! http://promo.yahoo.com/videomail/ -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body