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I have trouble getting the 20 Mhz oscillator to work with 16f877A Oscillator: Saronix 9942k 20.0000 Mhz NCH060C This is what I have done so far: 1) I connect the 20 Mhz oscillator to the OSC1 of the PIC and leave the OSC2 open. 2) I define my oscillator speed as follow: DEFINE OSC 20 since i use Pic Basic Pro compiler. I change my oscillator type to HS codes: DEFINE OSC 8 loop: high portb.0 pause 500 low portb.0 goto loop The above codes work fine with a 4Mhz oscillator but not the 20Mhz. How do I get the program to work with the 20Mhz oscillator? |
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20Mhz oscillator and 16f877
Started by ●August 13, 2003
Reply by ●August 14, 20032003-08-14
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> I have trouble getting the 20 Mhz oscillator to work with 16f877A > Oscillator: Saronix 9942k 20.0000 Mhz NCH060C Are you sure your osc does oscillate? Some have an enable pin, some don't. For the code: the only difference between the various crystal settings is the aplification, which should not matter because you use and external osc, not a crystal. So try with exactly the same code as you used for 4 MHz. Wouter van Ooijen -- ------- Van Ooijen Technische Informatica: www.voti.nl consultancy, development, PICmicro products |
Reply by ●August 14, 20032003-08-14
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Without a delay after "low portb.0" that is going to be a very narrow pulse. Something like 600 nS if the compiler generates good code. What are you using to check the output? --- In , "xeemv" <xeemv@y...> wrote: > I have trouble getting the 20 Mhz oscillator to work with 16f877A > Oscillator: Saronix 9942k 20.0000 Mhz NCH060C > > This is what I have done so far: > > 1) I connect the 20 Mhz oscillator to the OSC1 of the PIC and leave the > OSC2 open. > 2) I define my oscillator speed as follow: DEFINE OSC 20 since i use Pic > Basic Pro compiler. I change my oscillator type to HS > > codes: > > DEFINE OSC 8 > > loop: > high portb.0 > pause 500 > low portb.0 > goto loop > > The above codes work fine with a 4Mhz oscillator but not the 20Mhz. > > How do I get the program to work with the 20Mhz oscillator? |
Reply by ●August 14, 20032003-08-14
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I had problems some time ago with a canned oscillator check with a scope the voltage levels. Sometimes there are not CMOS levels --- In , "xeemv" <xeemv@y...> wrote: > I have trouble getting the 20 Mhz oscillator to work with 16f877A > Oscillator: Saronix 9942k 20.0000 Mhz NCH060C > > This is what I have done so far: > > 1) I connect the 20 Mhz oscillator to the OSC1 of the PIC and leave the > OSC2 open. > 2) I define my oscillator speed as follow: DEFINE OSC 20 since i use Pic > Basic Pro compiler. I change my oscillator type to HS |
Reply by ●August 15, 20032003-08-15
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hi xeemv, i too used 16F877A with 20MHz and PBP. i too had problem getting 20MHz crystal to work. here are some recommendations based on my similar experience: first, check your PIC chip to make sure it works at 20MHz. i know that 16F877A is rated for up to 20MHz as per the datasheet, but if you ordered the free sample version from Microchip there is a likely chance you received some of their old batch that they try to give out first, obviously, which is rated for 4 MHz only! you can determine if you have a 20MHz version by reading the Part Number stamp on your chip, it should read something to the effect of: "PIC16F877A-I20" or something like that. there should be a "20" near the end and not a "04". also, you provided Basic code in your message that says you defined operation for 20MHz. but in your cut/paste code snippet i see you defined for 8MHz. it should read: DEFINE OSC 20 not DEFINE OSC 8 do not forget that crystal oscillators require two capacitors. i found that my 28pF caps worked great with 4 MHz, but did not work at 20MHz. i switched capacitors to 10pF and it started working. good luck slloyd --- In , "xeemv" <xeemv@y...> wrote: > I have trouble getting the 20 Mhz oscillator to work with 16f877A > Oscillator: Saronix 9942k 20.0000 Mhz NCH060C > > This is what I have done so far: > > 1) I connect the 20 Mhz oscillator to the OSC1 of the PIC and leave the > OSC2 open. > 2) I define my oscillator speed as follow: DEFINE OSC 20 since i use Pic > Basic Pro compiler. I change my oscillator type to HS > > codes: > > DEFINE OSC 8 > > loop: > high portb.0 > pause 500 > low portb.0 > goto loop > > The above codes work fine with a 4Mhz oscillator but not the 20Mhz. > > How do I get the program to work with the 20Mhz oscillator? |
