Question About CMOS

Discussion in 'The Projects Forum' started by willgtl, Mar 23, 2015.

  1. willgtl

    Thread Starter New Member

    Sep 20, 2011
    I have an old Heathkit ID5001-C weather station and I wanted to clone the eprom. The eprom in question is an AMD AM27C256DC. Every part number I've seen is longer and includes the speed.

    Would the Atmel AT27C256R-45PU work? Does the speed matter or does 45ns work? Thanks!
  2. JDT

    Well-Known Member

    Feb 12, 2009
    You will have to check the data-sheets. Usually if the replacement is as fast or faster than the original there will be no problems.

    How are you actually going to do the copying? Do you have a programmer?
  3. willgtl

    Thread Starter New Member

    Sep 20, 2011
    Thanks. Unfortunately the chip only says AM27C256DC and doesn't specify the speed, nor does the manual for the machine and none of the old Heathkit resources on the internet specify it either. Considering the fastest AM27C256 is 50ns, would the 45ns Atmel chip work?

    And yeah, I bought a Signstek universal USB programmer.
  4. MrChips


    Oct 2, 2009
    When UVEPROMs were first developed access times were relatively slow, about 450ns. So anything today would be much faster than that.
    Be aware that back then, markings were different.
    -45 meant 450ns
    -20 would be 200ns

    Now that that would cause major confusion, today, -45 means 45ns.

    I doubt that a Heathkit of that era would have been using anything faster than 100ns.
    willgtl likes this.