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I own a couple of PS/2 to USB adaptor/converter connectors that look like the following:

Is there anyway to test if these adapters are passive without disassembling them (or risking damage by disassembly)? In all likelihood, they are passive as the active converters usually have a chip of some kind embedded in a cable to actively convert the protocol.

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  • \$\begingroup\$ All the active converters I've seen go the other way: Plug a PS/2 keyboard into a USB port. \$\endgroup\$ – markrages Apr 22 '11 at 23:04
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We pulled apart one of those and it's all wire or passive. The mouse that they come with must detect what it's plugged into USB or PS2 and do the right thing.

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  • \$\begingroup\$ right on. there's no way a PS2 mouse or keyboard port is going to operate a USB device. the ones of these that i've seen came with M$ mice, that could tell which kind of port they were connected to. \$\endgroup\$ – JustJeff Apr 23 '11 at 0:05
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All USB mice are capable of sending to a PS/2 port. This was by design because there are still many people who need to use PS/2 (for KVM's and such), but it is not reasonable for companies to continue to manufacture 2 separate items. Because of this, adapters like those are purely passive as the mouse itself is the one that figures out what it is connected to.

However, it doesn't work the other way around since PS/2 devices never had any idea of what USB was.

I did come across something interesting though, it looks as though you can plug a flash drive into a USB->PS/2 converter and then plug that into a PS/2->USB converter. Not really sure how that actually works though.

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  • \$\begingroup\$ That must be passive on both ends. There's almost no logical reason for a PS/2 -> USB converter to detect USB on the input and pass it through. There's not a chance in hell that you can plug one half of a differential asynchronous massively complex serial bus into a synchronous bus' clock IO pin and the other half into it's data IO pin and expect anything remotely correct to happen. \$\endgroup\$ – darron Apr 23 '11 at 17:15
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    \$\begingroup\$ All USB mice are capable of sending to a PS/2 port <sup>Citation needed</sup>. Why is this still true, since PS/2 has practically disappeared from modern motherboards? \$\endgroup\$ – Kevin Vermeer Jun 16 '11 at 14:12
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    \$\begingroup\$ @Kevin Vermeer I actually doubt that it is true... I know I did lots of googling before posting this answer and found a place that said it was part of the USB mouse and keyboard standard that it had to be capable of using ps/2... i cant find that now though. Wikipedia says that "many" do, but has no citations. \$\endgroup\$ – Kellenjb Jun 16 '11 at 14:19
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    \$\begingroup\$ Heh, how are they practically gone from modern motherboards. The last new computer I got (~year ago) came with a PS/2 keyboard. My computer I built 6 months ago has PS/2 support. I'm typing this on a PS/2 keyboard and using a PS/2 mouse. I think PS/2 is on it's way out, but it's definitely not going to die like floppy disks for probably another decade \$\endgroup\$ – Earlz Sep 26 '12 at 3:34
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    \$\begingroup\$ Data point: I just tested two USB mice. One cheap Logitech one from ~2009 and one expensive Razor one from ~2013. The old one does work correctly through a PS/2 passive adapter. The new one does not. \$\endgroup\$ – mgiuca Aug 22 '15 at 8:15

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