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Edit: Sorry, had messed up the capacitor values as I didn't take into account the values halve per leg. This should be fixed now...

I'm needing to attach a crystal to a microcontroller (a PIC16F84A), but the crystals I'm looking at are the 32.768Khz crystals which have either a 6pF, 12pF or as 12.5pF load capacitance. The thing is, I cannot get any capacitors with those values, the closest I can get is a 6.8pF10pF (5pF per leg), a 15pF (7.5pF per leg) and a 10pF respectively22pF (11pF per leg). Also, the datasheet for the microcontroller says that when running at 32kHz it recommends I use 68-100pF for each capacitor. So:

  1. Is the datasheet for the microcontroller really specifying a 32Khz crystal, or is it standard to refer to 32.768 crystal as a 32kHz crystal?

  2. Would the capacitors I can actually buy (6.8pF10, 15 and 10pF22 pF) be suitable, when considering the crystal is specifying slightly different values?

  3. Why are the capacitor values specified on the microcontroller datasheet so wildly different from those specified by the crystal? Surely only one of them can be correct, and what effect would this have if one of them is ignored?

Thank you!

I'm needing to attach a crystal to a microcontroller (a PIC16F84A), but the crystals I'm looking at are the 32.768Khz crystals which have either a 6pF, 12pF or as 12.5pF load capacitance. The thing is, I cannot get any capacitors with those values, the closest I can get is a 6.8pF, and a 10pF respectively. Also, the datasheet for the microcontroller says that when running at 32kHz it recommends I use 68-100pF for each capacitor. So:

  1. Is the datasheet for the microcontroller really specifying a 32Khz crystal, or is it standard to refer to 32.768 crystal as a 32kHz crystal?

  2. Would the capacitors I can actually buy (6.8pF and 10pF) be suitable, when considering the crystal is specifying slightly different values?

  3. Why are the capacitor values specified on the microcontroller datasheet so wildly different from those specified by the crystal? Surely only one of them can be correct, and what effect would this have if one of them is ignored?

Thank you!

Edit: Sorry, had messed up the capacitor values as I didn't take into account the values halve per leg. This should be fixed now...

I'm needing to attach a crystal to a microcontroller (a PIC16F84A), but the crystals I'm looking at are the 32.768Khz crystals which have either a 6pF, 12pF or as 12.5pF load capacitance. The thing is, I cannot get any capacitors with those values, the closest I can get is a 10pF (5pF per leg), a 15pF (7.5pF per leg) and a 22pF (11pF per leg). Also, the datasheet for the microcontroller says that when running at 32kHz it recommends I use 68-100pF for each capacitor. So:

  1. Is the datasheet for the microcontroller really specifying a 32Khz crystal, or is it standard to refer to 32.768 crystal as a 32kHz crystal?

  2. Would the capacitors I can actually buy (10, 15 and 22 pF) be suitable, when considering the crystal is specifying slightly different values?

  3. Why are the capacitor values specified on the microcontroller datasheet so wildly different from those specified by the crystal? Surely only one of them can be correct, and what effect would this have if one of them is ignored?

Thank you!

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R4D4
R4D4
  • 249
  • 3
  • 10

Matching load capacitors to crystal

I'm needing to attach a crystal to a microcontroller (a PIC16F84A), but the crystals I'm looking at are the 32.768Khz crystals which have either a 6pF, 12pF or as 12.5pF load capacitance. The thing is, I cannot get any capacitors with those values, the closest I can get is a 6.8pF, and a 10pF respectively. Also, the datasheet for the microcontroller says that when running at 32kHz it recommends I use 68-100pF for each capacitor. So:

  1. Is the datasheet for the microcontroller really specifying a 32Khz crystal, or is it standard to refer to 32.768 crystal as a 32kHz crystal?

  2. Would the capacitors I can actually buy (6.8pF and 10pF) be suitable, when considering the crystal is specifying slightly different values?

  3. Why are the capacitor values specified on the microcontroller datasheet so wildly different from those specified by the crystal? Surely only one of them can be correct, and what effect would this have if one of them is ignored?

Thank you!