Hi all
I just started working on an idea based around a PIC processor from Microchip. I used all kinds of components from my drawer, and got a surprice - I used a 8Mhz crystal from a TV set, which oscillates but at a low amplitude. The PIC does not start up.
Then I used a 4.9Mhz which gives a bigger amplitude at it works
What exactly is the difference in crystals?
Is there any literature on this?
WBR Sonnich
On a sunny day (Sat, 11 Apr 2015 01:26:36 -0700 (PDT)) it happened Sonnich Jensen wrote in :
Did you use the right capacitors, for example for the 16F628A:
TABLE 14-2: CAPACITOR SELECTION FOR CRYSTAL OSCILLATOR Mode Freq OSC1(C1) OSC2(C2) LP 32 kHz 15 - 30 pF 15 - 30 pF 200 kHz 0 - 15 pF 0 - 15 pF XT 100 kHz 68 - 150 pF 150 - 200 pF 2 MHz 15 - 30 pF 15 - 30 pF 4 MHz 15 - 30 pF 15 - 30 pF HS 8 MHz 15 - 30 pF 15 - 30 pF 10 MHz 15 - 30 pF 15 - 30 pF 20 MHz 15 - 30 pF 15 - 30 pF Note: Higher capacitance increases the stability of the oscil- lator but also increases the start-up time. These values are for design guidance only. A series resistor (RS) may be required in HS mode as well as XT mode to avoid overdriving crystals with low drive level specifica- tion. Since each crystal has its own characteristics, the user should consult the crystal manufacturer for appro- priate values of external components.
14.2.3 EXTERNAL CRYSTAL OSCILLATORSee datasheet.
Might not be the crystal but the PIC oscillator, you might need to change the config "fuse" bits to select HS oscillator type instead of XT type.
piglet
Have something to add? Share your thoughts — no account required.
Ask the community — no account required