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1.8V SDcards? — Parallax Forums

1.8V SDcards?

LoopyBytelooseLoopyByteloose Posts: 12,537
edited 2013-02-16 16:15 in General Discussion
With the coming soon Propeller 2, there is going to be a shift to 1.8 volts for the processor's i/o

It seems some, but NOT all of the SDcards sold can operate directly from 1.8volts, and some may even be dual voltage at 1.8 and 3.3 volt operation.

The thing is that I am not clear on
a. How to identify 1.8 volt compatible SDcards
b. Where to buy 1.8 volt compatible SDcards
c. How to properly wire up 1.8 volt compatible SDcards.

Sure, I could just assume the wiring is the same, but is it really? It would seem at least that the values of pull up and pull down resistors might change. Timiing might be slower as well.

Alternatively, can someone suggest a way to drive a 3.3v SDcard i/o with a 1.8v device?

Comments

  • doggiedocdoggiedoc Posts: 2,243
    edited 2013-02-16 04:19
    I imagine the solutions will be similar to how we deal with 5v devices and sensors with the 3.3v prop1. Level shifters.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-02-16 04:41
    Well, several other devices have claimed that one can simply buy a dual voltage 1.8v/3.3v SDcard and use it directly with a 1.8 volt device.

    But then, the search engines such as Googles show a lot of complaints and confusion about what is available and how such items are to work properly.

    I suspect the most conservative approach is to provide an interface for a standard 3.3 volt SDcard and forget trying to do something simpler.... at least until the retail vendors are aware there is a demand for a special 1.8 volt device.

    Some discussion of the dual voltage SDcards claim you have to start them with 3.3volts and switch to 1.8 volt power. That would be awkward, might as well stay with 3.3V and use level shifters.

    And others claim that dual voltage MMCcard are superior to dual voltage SDcards. I can't find an MMCcard on the store shelves here.
  • localrogerlocalroger Posts: 3,451
    edited 2013-02-16 15:50
    I thought P2 was going to be dual voltage with each I/O bank optional for 3v3 or 1v8 outside voltage. A lot of logic other than SD cards won't work with 1v8 so the chip would be somewhat handicapped if it can't do 3v3 I/O.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-02-16 16:15
    Forgive me, but you are absolutely right. The Propeller 2 is to be a 1.8 volt core with 3.3 volt i/o as an available option. I had forgotten this as I have been looking at another processor that is solely 1.8 volts and thinking that I must find ways to fit everything to 1.8 volts.

    Thank Heavens that Parallax realizes thiat 3.3volts is still important..
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