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Crystal/Clock and Programmer interaction... — Parallax Forums

Crystal/Clock and Programmer interaction...

Ben KirkpatrickBen Kirkpatrick Posts: 7
edited 2007-07-10 19:32 in General Discussion
··· I've made a mistake or two recently pulling&plugging the·oscillator to modify the program on an SX28.· The only way I know for sure is that the half-can got extremely hot and the project wasn't working.· I'd like to find a way to leave the osc in place but to disable it.· It might have /ENABLE on pin 1... (it's a Crystek 50mhz half-can, can't find docs for it anymore).
http://www.opamp-electronics.com/catalog/images/50_MHz_Half_Can_Oscillator_012820.gif

··· Has anyone figured out a way to disable/disconnect your clock source as soon as you see VPP on OSC1? (or was it OSC2?)

··· Also, what OSC setting is recommended for TTL clock source?· I've been using "OSCHS1" and it works most of the time.· Just want to confirm that it's correct.· SX28 datasheet was a little vauge, even with the Transko 75Mhz example.

Thank,
--Ben

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2007-07-09 04:03
    A two-pin header between the OSC's output and the SX OSC input.· Then, place/remove a "jumper block" to complete/interrupt the connection.· It's not idiot proof, but it's easier than cranking out the OSC.·

    I think it's best form to power off the SX before you connect/disconnect the SX-Key.
  • BeanBean Posts: 8,129
    edited 2007-07-09 12:15
    I don't think using the /ENABLE pin would work. Even if the oscillator is not enabled, it still isn't going to like +12V applied to it's output pin.

    I use the same device setting that I would if I was using a resonator. So OSCHS2 for 50MHz.

    Bean.

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  • DosManDanDosManDan Posts: 179
    edited 2007-07-09 17:52
    You might want to try my approach. Make a little board, for the oscillator, that plugs into the 4 pin header used to program the SX chip. You have to unplug it before you can program, so you can't use the two at the same time. It's also easy to switch oscillators using the approach.

    Dan
  • pwillardpwillard Posts: 321
    edited 2007-07-10 14:38
    You know... I really like that idea.· Especially when using a can oscillator.· The only problem I see for me is coming up with a nice 4 pin female header that's small on real-estate and doesn't need to be hacksawed to death to make it work.
  • PJMontyPJMonty Posts: 983
    edited 2007-07-10 19:32
    Just to confirm, you can't use the ENABLE line on TTL oscillators and have the SX work right. You must physically disconnect the oscillator's clock output from the SX clock input before using the SX-Key.

    How do I know? Experience with a PCB I designed and had manufactured before testing the ENABLE concept. Fortunately, I only had three prototypes made, so the investment wasn't that high.

    Thanks,
    PeterM
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