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caps not pop with watch crystal

You can find this sentence in ADuC 841 evaluation board schematic. Could someone explain what does it mean?

  • 2
    \$\begingroup\$ If you don't put in a watch crystal the capacitors might explode? \$\endgroup\$ Commented Mar 15, 2016 at 14:41

1 Answer 1


The ADuC 841 integrated circuit will work with either of two alternative crystals. The ADuC 841 evaluation board (for which the schematic notes have precipitated the question) has therefore been designed to take either of those crystals. It has footprints for capacitors C17/18, which depending on which crystal is fitted can be either populated or left unpopulated.

If you fit the 11MHz one, you must also fit the capacitors.

If you fit the 32768Hz one (a 'watch' crystal) you must not fit the capacitors. Pop is an abbreviation for populate.

  • \$\begingroup\$ I guess my answer was not clear enough? \$\endgroup\$
    – Armandas
    Commented Mar 14, 2016 at 19:21
  • \$\begingroup\$ Neil also notes that the user must use ONE of the crystals, an information which the OP seems to have missed, so I guess his answer is more complete. \$\endgroup\$ Commented Mar 14, 2016 at 19:28
  • \$\begingroup\$ I find Neil's answer to be simpler and more comprehensive. I didn't missed the fact that only one crystal must be used -- it wouldn't make sense to have both of them. \$\endgroup\$ Commented Mar 14, 2016 at 19:34
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    \$\begingroup\$ Anyway thank you both, as non-native english speaker (and electronics hobbyist) I would never guess that "pop" is for populate ;) \$\endgroup\$ Commented Mar 14, 2016 at 19:36
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    \$\begingroup\$ @Armandas: The "pupulated" spelling didn't help your cause either. ;^) \$\endgroup\$
    – Transistor
    Commented Mar 14, 2016 at 20:37

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