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loss of power? — Parallax Forums

loss of power?

D FaustD Faust Posts: 608
edited 2007-08-21 23:09 in General Discussion
What would happen if an SX is cut off from vdd but not vss.· Would the pins got to ground, float, or would you have a·fried SX.· I do not have an SX, but I do have a pwmpal, which uses an SX.

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Comments

  • JonnyMacJonnyMac Posts: 9,216
    edited 2007-08-21 18:08
    I was working on a LanC camera controller that took power from the camera, and had an I/O pin connected to the camera's serial I/O pin. When the camera was told to power down it would, then come back on about two seconds later -- this behavior is indicative of the serial line being shorted to ground, so I suspect that's where my SX I/O went. In the end I had to use the transistor buffer circuit recommended by Sony in their LanC specification.
  • D FaustD Faust Posts: 608
    edited 2007-08-21 18:20
    You are saying that you still had 5V to the SX, but no ground so the pin shorted to ground, correct?

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  • BeanBean Posts: 8,129
    edited 2007-08-21 18:55
    If you have any I/O pins connected to another power source, the power will feed back through the I/O pin protection diodes and power the circuit. The power source could be a serial output from another device.

    Bean.

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  • D FaustD Faust Posts: 608
    edited 2007-08-21 19:45
    Thanks, I would be inputting data serially so·I guess·what I was trying to do·wouldn't work.· (setting the pins to·ground by cutting vdd)


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ON subnum GOTO Hope_this_helps, Thanks!, WOW!!
END
  • JonnyMacJonnyMac Posts: 9,216
    edited 2007-08-21 20:20
    D Faust said...
    You are saying that you still had 5V to the SX, but no ground so the pin shorted to ground, correct?

    No, when the camera shuts down the external 5v pin goes dead, my SX went dead, then the camera came back to life because its LanC pin was shorted to ground (this is expected behavior, but I didn't want it in my circuit, hence the transistor buffer).
  • D FaustD Faust Posts: 608
    edited 2007-08-21 21:18
    Okay, so everything went dead and the pin was shorted to ground, right?

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    LOOKDOWN ThisThread, [noparse][[/noparse]Your_?, My_?, Cool_Thing], looknum
LOOKUP looknum, [noparse][[/noparse]1, 2, 3], subnum
ON subnum GOTO Hope_this_helps, Thanks!, WOW!!
END
  • JonnyMacJonnyMac Posts: 9,216
    edited 2007-08-21 23:03
    In my case that seems to be what happened.
  • D FaustD Faust Posts: 608
    edited 2007-08-21 23:09
    As I stated earlier, what Bean told me ended my aspirations anyway, but thanks for the help.

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    LOOKDOWN ThisThread, [noparse][[/noparse]Your_?, My_?, Cool_Thing], looknum
LOOKUP looknum, [noparse][[/noparse]1, 2, 3], subnum
ON subnum GOTO Hope_this_helps, Thanks!, WOW!!
END
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