The Pesky PWDIS Feature In Newer SATA Specs

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takeshi7

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This is a stupid problem that could have easily been avoided if they would have made it when the pin is LOW instead of HIGH. What stupid committee decided this?

Why would you make a pin HIGH voltage to enable a power saving function? That is the opposite of what you want when you try to save power.
 

anbello262

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I agree that this would solve the issue almost completely. The only problem would be that you would no longer be able to use molex-to-sata adapters with those discs, but that is a MUCH smaller issue.
 

wuethrichtech

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@takeshi7 i havent read the spec but my guess is less than 0.005 amps flow. resistors resistors resistors.... its a signal not a power power flow. see e=i*r and p = e*i.

@toms... dangerous shorts?can you give an example of what isnt protected on this supply? sure its not great to let it happen as a general rule of thumb or to trust a bot of line psu to kill the rail or turn off. thats not what you are reviewing though. short that puppy out and tell us how it does. Or maybe show people how to use a soldering iron and heat shrink tube
 

linuxgeex

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I'm guessing you could also snip the wire to that pin. If the molex is working simply due to lack of connection then severing the connection would have the same result... use a pin to separate the ribbon, cut 2-3mm out of that wire, job done.
 

chaz_music

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Takeshi7 is right. As I read the article, I thought the same thing. Making the signal active low = HDD reset would make this 100% backwards compatible to the older PSU's having 3.3V on that pin. Did anyone do a design review on this spec change? And on another note, if I am thinking right, you could also snip the orange wire going to the SATA power connector and tape up the wire ends to fix this as well. As long as the HDD does not use 3.3V.
Aris: Is the 3.3V pin used on SSD's? And is this feature for PWDIS to be used on SSD's? And how is the signal supposed to get to the SATA power connector from the motherboard? The SATA power usually comes directly from the PSU.
 

plateLunch

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There must have been some thinking behind this. They kind of went against convention with this one. Most of the reset signals I see on ICs and busses are active low. Makes it easy to use an open drain/open collector driver with a pullup to drive the reset signal. I hope this wasn't a consequence of the name (PWDIS) and the desire to use positive logic. Something like that coming out of a standards organization sends chills down my spine.
 

compprob237

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A simple change to what Takeshi7 said would solve a lot of the problems this presents. Pair that with a jumper to disable the feature completely and you've solved the problem outright.
 

alextheblue

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Chances are extremely good that if you're using modern PWDIS drives you're powering them with SATA connectors. However, for those who just don't have enough SATA connectors, have molex 4-pins to spare, and are driving PWDIS drives: They could have released a PWDIS compatible molex-sata adapter that has a simple voltage converter integrated to generate the 3.3V required. Cheap, simple, compact, reliable. Slap a PWDIS warning on the drives - "WARNING: Do not use Molex-to-SATA adapters with this drive unless they are PWDIS Certified" or whatever.
I would do that with an inexpensive extension maybe - don't want to damage the PSU's cabling itself if I don't have to. But the issue is awareness... a lot of people simply aren't going to be aware that they did something so UNBELIEVABLY STUPID in the newer specs.
 

alextheblue

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A jumper. Good call... I'd say regardless of whether they chose high or low, a jumper to enable/disable PWDIS should have been mandatory to meet the new spec and set to PWDIS disabled by DEFAULT with documentation included to make installers aware the feature exists - if they care and want it enabled.
 

Aris_Mp

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SSD's the 2.5" ones don't use 3.3V as far as I know, but 5V. Only a number of the 1.8" ones do use this rail. Our storage editors will know more on this matter actually since it has been ages till the last time that I reviewed an SSD..
 

chaos133

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I found the answer to my own question here in case if anyone else wants to know.

Q: If I install a drive with the feature into a system that does not
support it (or vice versa), can I damage the HDD?
A: No. You can safely plug an HDD either with or without the feature into
a new or legacy system.

If the legacy system is providing power to P3 (Pin 3), the only side effect
is that the HDD will not spin up.

Likewise, if you have a new chassis that supports the Power Disable
feature, an HDD without the feature will just ignore the Hard Reset
request and remain powered up.


 

braitBR

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Since the power plug for SATA drives has a gazillion unused pins.... Why not use one of them? Power supplies compatible with PWDIS would have the new plug and olders ones wouldn't. There. 100% backward and forward compatibility.
 

chaz_music

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Aris, where does the PWDIS signal originate? Usually, the SATA power connector comes directly from the PSU, but I would expect the signal to come from the motherboard so the OS can actively reset a HDD. Is there a new cable that comes from the MB to the PSU so it can be routed into the SATA power cables?

I do see this as a very useful feature, since it is not unusual for a HDD stop responding after being hot plugged into an AHCI SATA port. The logic level issue seems like it came down to making a last minute decision before posting the spec and they goofed.
 
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