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using pins 30 and 31 — Parallax Forums

using pins 30 and 31

bozobozo Posts: 70
edited 2007-08-28 17:20 in Propeller 1
Hi,
the manual says these pins are free to use for other purposes after they've loaded the eeprom, but what prevents interference from the eeprom after booting? Are there any hidden traps in using these pins?
Cheers,
Mark

Comments

  • R PankauR Pankau Posts: 127
    edited 2007-08-28 16:16
    I'm no expert but I may have one answer,
    the EEprom is hardware addressable (3 bits worth) they are all tied to ground so as long as you don't request any data from that chip's addres it should be silent. you could put other EEPROMs on the same bus as long as they had different addresses as set by the 3 external pins.

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    necessity is a mother
  • deSilvadeSilva Posts: 2,967
    edited 2007-08-28 16:17
    bozo said...
    Are there any hidden traps in using these pins?
    There are traps, but they are by no means "hidden". Just have a look at the schematic and you will soon be able to anwer yiur question yorself.

    They form a pair of I2C lines and you should not apply signals to them the EEPROM could mistake for a correctly addressed access.
  • bozobozo Posts: 70
    edited 2007-08-28 16:26
    so if I use these pins for sending random data (say), there's always going to be a small probability that the bit streams might prod the eeprom into action unintentionally?
  • Paul BakerPaul Baker Posts: 6,351
    edited 2007-08-28 16:34
    Yes, you can use either one for any use with no problem, or use both as an I2C bus for other I2C devices, but using both for any purpose runs the risk of getting the eeprom to respond with a memory location (producing indeterminate signal behavior) or writing to a memory location (potentially catostrophic program alteration).

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    Paul Baker
    Propeller Applications Engineer

    Parallax, Inc.
  • deSilvadeSilva Posts: 2,967
    edited 2007-08-28 16:35
    A VERY small probability. But note you have also things like a pull-up....
  • Paul BakerPaul Baker Posts: 6,351
    edited 2007-08-28 17:00
    Technically it's a 1 in 256 chance for the EEPROM chip used on the protoboard for any set of 8 cycles on the SCL, that is not an exceeding small statistic when you consider you are potentially rolling the dice hundreds of times a second.

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    Paul Baker
    Propeller Applications Engineer

    Parallax, Inc.
  • parts-man73parts-man73 Posts: 830
    edited 2007-08-28 17:05
    The Boot EEPROM is attached to P28-P29, not 30 and 31.

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    Brian

    uController.com - home of SpinStudio
  • R PankauR Pankau Posts: 127
    edited 2007-08-28 17:20
    it was a trick question

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    I'd rather have a bottle in front of me than a frontal labotomy
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