USB -> PS/2 pin connections?

[spremino]

Hello,

I'd like to connect a USB keyboard to a PS/2 circuit using just a USB female socket (that is, I don't want to go through a passive USB to PS/2 adapter). I've not been able to find how pins relate to each other. Of course, I'm talking about a keyboard which supports both protocols.

Any help?

Thanks

[ch_123]

It's not a straightforward conversion - USB has two data pins, Ground and 5V. PS/2 has 5V, data, Ground and Clock. If your keyboard supports both, I'm guessing that one of the USB data lines is really the clock line.

What sort of keyboard is it? Does the manufacturer not provide more details?

[Rajagra]

Testing continuity on a passive convertor...

usb socket - ps/2 plug

ground-ground   (shields)
1-5
2-6
3-4
4-2

USB numbering is looking into the USB socket with contacts facing up, 1 is on left to 4 on right.

PS/2 numbering is looking into the plug with the plastic notch down, 1 is bottom left, go clockwise to 6 at bottom right.

This is not the standard numbering system!!!

I get the same results testing a purple keyboard convertor and a green mouse convertor. (I've always wondered if they were the same.)

EDIT> You can see the conventional numbering here: http://pinouts.ru/InputCables/usb_ps2_mouse_pinout.shtml
It does match what I said! :-)

[quadibloc]

I'd like to connect a USB keyboard to a PS/2 circuit using just a USB female socket (that is, I don't want to go through a passive USB to PS/2 adapter).

That is not possible. A USB keyboard produces signals which cannot be decoded by a PS/2 interface, and it also may consume more power than a PS/2 port can supply. USB to PS/2 adapters are not passive - they convert the scan codes and the signal protocol.

[timw4mail]

That is not possible. A USB keyboard produces signals which cannot be decoded by a PS/2 interface, and it also may consume more power than a PS/2 port can supply. USB to PS/2 adapters are not passive - they convert the scan codes and the signal protocol.

They're awfully small, cheap, and common for that to be the case.

[Special K]

That is not possible. A USB keyboard produces signals which cannot be decoded by a PS/2 interface, and it also may consume more power than a PS/2 port can supply. USB to PS/2 adapters are not passive - they convert the scan codes and the signal protocol.

I'm not even sure I understand what the OP is asking for.  If you want to convert a USB keyboard to use with a PS/2 port, can't you just use one of these:



Those are the kind packaged with Filcos and they look passive to me.

I thought converting a PS/2 keyboard to USB required an active adapter such as the blue cube:



Something like this wouldn't work:



Am I correct?  Why is it that converting a USB keyboard to PS/2 can be done passively, but converting a PS/2 keyboard to USB requires an active adapter?

[Rajagra]

You can't convert either way passively.
The passive adapters only work with dual-mode devices that detect which interface is being used, then send signals accordingly.

[Special K]

You can't convert either way passively.
The passive adapters only work with dual-mode devices that detect which interface is being used, then send signals accordingly.

Ah, that makes sense.  So why are the adapters I posted in pictures 1 and 3 even sold as standalone items?  Are consumers supposed to know that they need a dual mode keyboard/mouse to use them?

What happens if you try to use one of those adapters with a keyboard or mouse that isn't dual mode?  Will it ever work at all?

[Rajagra]

Some people might have lost the adapters that came with their dual-mode keyboards/mice. The adapters won't work if the device isn't dual-mode, but the good news is at least you won't fry the ports because 0V goes to 0V and +5V goes to +5V, etc.