Level conversion for PMOS ROM

Discussion in 'The Projects Forum' started by skot9000, Mar 7, 2012.

  1. skot9000

    Thread Starter Member

    Jan 28, 2009
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    Hello,

    I am trying to interface with an ancient (from 1980!) PMOS ROM that uses -9V as logic low and 0V as logic high. Does anyone know of a way to do bi-directional voltage level conversion to use this with a more common 5V microcontroller?

    Thanks!
    -Skot
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    What speed are we talking about here?

    Do you have a datasheet of the ROM?
     
  3. skot9000

    Thread Starter Member

    Jan 28, 2009
    18
    0
  4. skot9000

    Thread Starter Member

    Jan 28, 2009
    18
    0
    Also, BTW, I'm pretty sure in section 3.2 of the datasheet there is a small typo. Vdd should have a range of -8.3V to -9.7V (NOT -8.3V to 9.7V)
     
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,394
    1,607
    The simplest way to start is ground the -9V Vdd and connect ground to +9V.

    That way at least the signals are above ground, logic zero is zero, and you only have to divide or scale up the ones.
     
  6. skot9000

    Thread Starter Member

    Jan 28, 2009
    18
    0
    Awesome! I think this is the right idea. It looks like will even be able to use regular 5V logic this way, albiet inverted.

    thanks!
     
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