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Prop Chip SCL I2c Line shorted to VSS... but can't find short? Chip broken? — Parallax Forums

Prop Chip SCL I2c Line shorted to VSS... but can't find short? Chip broken?

KyeKye Posts: 2,200
edited 2009-08-13 18:03 in Propeller 1
Has anyone had this problem?

Everything was working fine until I attached a DS1307 5V I2C device. Now the SCL line is shorted to ground. I have removed the connection but the short still exist. Is it possible I have broken one of the parts?

The thing is that the I2C line is open drain so there should be no problems with a 5V device.

Anyone else had this happen to them? Solutions?

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Nyamekye,

Comments

  • KyeKye Posts: 2,200
    edited 2009-08-13 16:34
    And, yes the prop chip still works but I get an eeprom program error when I try to program the eeprom.

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    Nyamekye,
  • Mike GreenMike Green Posts: 23,101
    edited 2009-08-13 16:43
    The Prop I/O pin circuitry is pretty robust and is generally tolerant of short-circuit type abuse. I think Paul Baker did some testing along this line and found that he could short circuit an I/O pin to either Vss or Vdd indefinitely without apparent damage (with the pin set to output the opposite state). Check for damage to the PCB or other shorts external to the Prop.
  • KyeKye Posts: 2,200
    edited 2009-08-13 16:47
    Could it be the eeprom?

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    Nyamekye,
  • Mike GreenMike Green Posts: 23,101
    edited 2009-08-13 16:53
    It could be the EEPROM although, like you, I wouldn't expect a significant potential for damage given that the I2C bus is open-drain.
  • KyeKye Posts: 2,200
    edited 2009-08-13 17:07
    I scraped the copper base plane below the proto board and the solder attached to it. Thanks Mike,

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    Nyamekye,

    Post Edited (Kye) : 8/13/2009 5:46:14 PM GMT
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-08-13 17:11
    Looking at the datasheets, there's just nothing to indicate any kind of incompatibility between the DS1307 and the EEPROM. They should coexist peacefully on the same bus (pulled up to 3.3V, with the '1307 powered from 5V). I suspect you've introduced a short while soldering. Do you have a loupe that you can use to inspect your work? I've seen hair-thin wisps of solder cause this kind of thing.

    Anyway, I seriously doubt that any parts have been damaged.

    -Phil
  • AleAle Posts: 2,363
    edited 2009-08-13 17:31
    I'm working now with that part and found the truth that it is a 5V device. But the bus is open-collector/open-drain so why should an incompatibility between 5V-powered with 3V3-powered devices exist ?... It shouldn't.

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    Visit some of my articles at Propeller Wiki:
    MATH on the propeller propeller.wikispaces.com/MATH
    pPropQL: propeller.wikispaces.com/pPropQL
    pPropQL020: propeller.wikispaces.com/pPropQL020
    OMU for the pPropQL/020 propeller.wikispaces.com/OMU
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-08-13 18:03
    The only time a 5V device might have an issue with 3.3V signaling is when VIH(min) is near to or higher than 3.3V, which it is with many "HC" CMOS parts. But that's not the case with the DS1307, whose VIH(min) is a comfortably low 2.2V

    -Phil
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