What's the switch on HDD/DVD caddies for?
2 votes c/questions Posted by zPlus — 2 votes, 4 commentsSource

Has anyone used any of these hard-disk/dvd caddie adapters?

There’s a white 2-way switch on the side and I have absolutely no idea what it is for, or how I’m supposed to set it. I assumed these adapters where just basic PCBAs, with traces mapping the two SATA connectors one-to-one. Here are two pictures I took after disassembling it

I’ve just checked the pinout and it seems to be wired like this:

SATA Slimline pinout diagram
Pin     Name    Function
  1     GND     Ground
  2     A+      Transmit+
  3     A-      Transmit-
  4     GND     Ground
  5     B-      Receive-
  6     B+      Receive+
  7     GND     Ground

  8     DP      Device Presence
  9     +5V     5V Power
 10     +5V     5V Power
 11     M       Manufacturer diagnostic
 12     GND     Ground
 13     GND     Ground

Says RO, so read only? Might not be functional, only one way to find out.

They say to set it in the middle here: https://www.overclockers.com/forums/threads/drive-caddy-dip-switch-what-does-it-do.763426/

read only

interesting take. I interpreted it as R0 (R-zero), as in zero resistance.

In the SATA specs it seems to be called “manufacturing diagnostic pin” and from what I understand it’s an optional bit that is only used by some systems.

I tried switching it but I didn’t notice any apparent difference. My switch is only 2-ways, though, there’s no “middle” state.

Don’t what you are talking about at all. Just know that disks often support SMART and you said that the pin is for diagnostic. Maybe they are related?

No I don’t think this is correct. SMART is stored in the disk itself and can be read from it using the default transmission pins. This seems to be some kind of lower hardware-level type of diagnostic. Unfortunately it’s not documented anywhere.