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ide interface at 3.3V — Parallax Forums

ide interface at 3.3V

mctriviamctrivia Posts: 3,772
edited 2009-10-15 19:23 in General Discussion
Is it possible to communicate with a IDE hard drive using 3.3V signal levels? or do i need to some how shift the voltage up and down to 5v?

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Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2009-10-15 16:11
    It depends on the drive. Old drives designed before 3.3V devices were readily available might require 5V logic levels. Newer IDE drives would have I/O lines that can handle 5V or 3.3V. You'd have to look at the drive's datasheet.

    The IDE standard states that the logic high input voltage must be 2.0V or greater and guarantees 2.4V or greater for high outputs. This would be compatible with either 3.3V or 5V logic. Again, check the datasheet to make sure that the drive itself supports this.

    Post Edited (Mike Green) : 10/15/2009 4:23:19 PM GMT
  • mctriviamctrivia Posts: 3,772
    edited 2009-10-15 16:20
    ok so as long as i or anyone using my product is careful to use a newer drive that suports 3.3V there will be no problems? the drive will not try to output 5v and cause problems with the cmos ic?

    or do i need to use a series resister and clamp diode?

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    propmod_us and propmod_1x1 are in stock. Only $30. PCB available for $5

    Want to make projects and have Gadget Gangster sell them for you? propmod-us_ps_sd and propmod-1x1 are now available for use in your Gadget Gangster Projects.

    Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.
  • Mike GreenMike Green Posts: 23,101
    edited 2009-10-15 16:30
    As always, check the datasheet for the drive. It'll probably be ok, but I won't guarantee it.

    Whenever you (or anyone else) asks a question like this with a "there will be no problems?" part, the only answer you can reasonably get is "I don't know". I have no knowledge or control over what you're actually using or doing. I know that I would check the manufacturer's datasheet to assure myself that the device is supposed to behave the way I expect it to and I might test the device to make sure it behaves like the datasheet says, at least in ways that I feel are critical. If the manufacturer says it's designed to work with 3.3V and 5V controllers, I usually will believe them. If they don't say, I'll look at the detailed specifications, particularly the Vil, Vih and Vol, Voh which define the interface voltages used (and expected).
  • mctriviamctrivia Posts: 3,772
    edited 2009-10-15 16:34
    I guess I will look up several drives and see. I know the pc does not care what drive is used and I would like to be able to use any hard drive with my device also but could not find what the ide specs say

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    propmod_us and propmod_1x1 are in stock. Only $30. PCB available for $5

    Want to make projects and have Gadget Gangster sell them for you? propmod-us_ps_sd and propmod-1x1 are now available for use in your Gadget Gangster Projects.

    Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.
  • Mike GreenMike Green Posts: 23,101
    edited 2009-10-15 16:45
    There's a Wikipedia article on the IDE interface standard and it has links to the various generations of formal IDE specs. I had looked at ATA-4 for the voltage ranges I mentioned. The problem is that those voltages are minimums, so any output voltage greater than 2.4V would be within spec which includes voltages above 3.3V. I think you'd be safest with a just a series resistor (like 2.2K) since the Propeller has its own clamp diodes. These would slow down the bus due to RC effects, but they'd also dampen reflections and noise. You could use active level translators if you're concerned about speed. Look at the new Propeller Servo Controller and the StingRay controller for examples of these.
  • mctriviamctrivia Posts: 3,772
    edited 2009-10-15 16:49
    Actually using epm1270 as ide controller it also has built in clamping diodes.

    I will put the series resistors in. Can always populate with 0 ohm if it needs to be faster.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    propmod_us and propmod_1x1 are in stock. Only $30. PCB available for $5

    Want to make projects and have Gadget Gangster sell them for you? propmod-us_ps_sd and propmod-1x1 are now available for use in your Gadget Gangster Projects.

    Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.
  • Mike GreenMike Green Posts: 23,101
    edited 2009-10-15 17:37
    Read the datasheet very carefully! The built-in clamp diodes only work once the EPM1270 is powered up and you'd need external clamp diodes if the ATA (IDE) interface could possibly be powered up earlier.
  • mctriviamctrivia Posts: 3,772
    edited 2009-10-15 19:23
    thanks for the pointer. I will have to use a mosfet to keep the hard drive off until the system is up and ready.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    propmod_us and propmod_1x1 are in stock. Only $30. PCB available for $5

    Want to make projects and have Gadget Gangster sell them for you? propmod-us_ps_sd and propmod-1x1 are now available for use in your Gadget Gangster Projects.

    Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.
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