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Crystal Requirements — Parallax Forums

Crystal Requirements

dsmith23dsmith23 Posts: 1
edited 2006-11-11 00:56 in Propeller 1
·Are there any caveats to choosing an external·crystal for the Q-44 package...? We attempted to use a 5MHz / 20pF but the smd package of the prop did not seem to be agreeable whereas the 40 pin DIP package had no problems.....?

thanks in advance.....

Comments

  • cgraceycgracey Posts: 14,133
    edited 2006-11-10 21:59
    We've not noticed any such problems, and by design they shouldn't exist. Usually, a sagging power supply or lack of an external capacitor between VSS and VDD cause problems that look like that. Do you have adequate decoupling (1uF) on the -Q44 board, and is the power supply a stable 3.3V? Just checking.

    BTW, the crystal oscillator provides much more capacitive loading to the crystal than package-related parasitics introduce, so I'm thinking there was some other problem.

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    Chip Gracey
    Parallax, Inc.

    Post Edited (Chip Gracey (Parallax)) : 11/10/2006 10:13:03 PM GMT
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2006-11-11 00:56
    Also, if you're prototyping the Q44 circuit with a non-soldermasked PCB, make sure the crystal can doesn't touch any traces. Even with soldermask, I recommend a crystal insulator.

    -Phil
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