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compass module data in/out pins — Parallax Forums

compass module data in/out pins

damiondamion Posts: 39
edited 2007-05-15 06:43 in General Discussion
Hello,

I'm using the HM55B compass module. I want to tie the data in/out pins to the data in/out pins of some other SPI chips. Do I need to use a 1 kohm resistor in between them or can they be tied directly together?

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Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2007-05-15 06:43
    It depends on the other SPI chips. Some SPI devices are made to be able to tie the data in/out pins together and some are not (because they don't switch the output pin to a high impedance when the device isn't selected). Theoretically, you can tie all the data in/out pins together if the output pins are all tri-stated (made high impedance) when the devices are not selected. In practice you can do this if you are certain that you can't select two devices at the same time (like due to a programming error). If you're not certain, then you need some kind of series resistor to protect the output pins from a short circuit if one is high and another is low at the same time.
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