Is it possible? PS/2 to USB connector?!

[ali6x944]

Hi everyone,
I had a old keyboard laying around which have a PS/2 connector on it but my laptop doesn't have PS/2 connector so I ask Is it possible? PS/2 to USB connector?! Directly?

[coppice]

You can buy adaptors. The ones I have used have one USB connector and two PS/2 connectors - one for a PS/2 mouse and one for a PS/2 keyboard.

[Richard Crowley]

https://www.adafruit.com/products/971

[ali6x944]

Using this method:

[Monkeh]

Using this method:

No.

[suicidaleggroll]

I've purchased devices similar to the one posted by Richard Crowley many times, they work just fine.

[ali6x944]

Using this method:

No.

I've purchased devices similar to the one posted by Richard Crowley many times, they work just fine.

What so will it work or not?

[Richard Crowley]

The protocol used by the old PS2 keyboard/mouse is NOT the same as USB.
You cannot connect them straight across like that.
What we call the "PS2 protocol" is actually I²C. NOT compatible with USB.

Some modern USB keyboards have auto-sense and will work with a simple converter.
But it would be extraordinary to find an old PS2/I2C keyboard that would speak USB.
Especially since USB hadn't even been invented yet.
I strongly suspect there is a tiny protocol conversion chip in the USB plug that does the conversion.

[electr_peter]

Some mouse/keyboard devices support both PS/2 and USB on the same lines, thus making simple passive adapters (USB<->PS2) possible. Other devices require special active PS2<->USB converters.

One can always try to see if it works. PS2 is ancient, are you sure you really need it?

[wraper]

Using this method:

No.

I've purchased devices similar to the one posted by Richard Crowley many times, they work just fine.

What so will it work or not?

If this keyboard is less than 10 years old, quiet likely it will. The older is the keyboard, the less chance you have it working.

[Monkeh]

Using this method:

No.

I've purchased devices similar to the one posted by Richard Crowley many times, they work just fine.

What so will it work or not?

Wiring a PS/2 keyboard to a USB port is entirely different to using an active adapter.

You cannot wire a PS/2 keyboard to a USB port. You can wire some USB keyboards to PS/2 ports.

[suicidaleggroll]

Using this method:

No.

I've purchased devices similar to the one posted by Richard Crowley many times, they work just fine.

What so will it work or not?

Will what work?  I highly doubt the wiring schematic you posted would work at all, I wasn't talking about that.  The adapter posted by Richard Crowley does not just map pins, it does the full USB to PS/2 translation and works just fine.

[suicidaleggroll]

I strongly suspect there is a tiny protocol conversion chip in the USB plug that does the conversion.

Yes there absolutely is, it says so on the page you linked to:

Inside is a full translation chip - a small USB microcontroller that will translate the PS/2 into "USB Keyboard" and "USB Mouse"

[wraper]

Wiring a PS/2 keyboard to a USB port is entirely different to using an active adapter.

You cannot wire a PS/2 keyboard to a USB port.

Yes you can, manufacturers often use the same chipset and only connector is different.

You can wire some USB keyboards to PS/2 ports.

most of them

[Monkeh]

Wiring a PS/2 keyboard to a USB port is entirely different to using an active adapter.

You cannot wire a PS/2 keyboard to a USB port.

Yes you can, manufacturers often use the same chipset and only connector is different.

You can wire some USB keyboards to PS/2 ports.

most of them

Of the few dozen I have on hand? Maybe two or three USB ones which are definitely compatible (came with the adapter), most which are not, and a few PS/2 ones which mostly predate USB acceptance. So.. I disagree.

[ali6x944]

So I have to use a microcontroller of some kind to to connect from ps/2 to usb...

[Monkeh]

So I have to use a microcontroller of some kind to to connect from ps/2 to usb...

Or just buy the off-the-shelf adapter.

[ali6x944]

PS/2 pulgs uses I²C right?

[rsjsouza]

So I have to use a microcontroller of some kind to to connect from ps/2 to usb...

Or just buy the off-the-shelf adapter.

As others have said, an old PS/2 keyboard will not work if connected directly to a USB port such as this one - some more modern keyboards and mice would have the USB/PS/2 auto-sense circuitry mentioned.

You need an active microcontroller-based converter but several adapters will have some trouble with a 104-key ABNT2 keyboard - in my experience most of the keys will work but not the backslash and the period in the numeric keypad.

One adapter I use with my ABNT2 Model M keyboard is this one - all keys but the period on the keypad work. Make sure you get the version 2.0 of that.

 

[Ian.M]

PS/2 uses 5V signalling over a two wire open collector bus.  The clock is generated by the device but can be inhibited by the host.  the data line is bidirectional.   This is totally different from USB which uses 3.3V quasi-differential signalling.

Some keyboard and mouse chipsets during the transition period (round about the turn of the Millennium) when Microsoft & Intel were pushing the 'Legacy free PC' could do both, and detect what type of port they were connected to (quite easy - if pulled up to 5V talk PS/2 otherwise activate their USB SIE and gate it onto the bus), via a proprietary 'dumb'  adapter. 

I wouldn't expect most modern keyboards to support both protocols, and old ones from the early days of USB didn't either.   I seem to remember a lot of Logitech Keyboards/Mice from that era that supported both, but their adapters were usually not interchangable with other brands.  You'd need to check the user manual of the specific model device you have to see if there's any chance that a dumb adapter will work, then will have to get lucky and find an adapter with the correct (almost invariably undocumented) wiring for your device.

Dual interface mode keyboards and mice are nowadays only a historical curiosity.  You'd be far better off getting a budget USB keyboard or if you have a really nice legacy IBM or Cherry mechanical PS/2 keyboard, getting a smart USB <=> dual port Keyboard/Mouse adapter.

[Richard Crowley]

PS/2 pulgs uses I²C right?

Correct

[Ian.M]

PS/2 pulgs uses I²C right?

Correct

WRONG!  Its nothing like I2C apart from the open collector bus. A few of the differences are no addressing, different framing and ACK.
See http://computer-engineering.org/ps2protocol/

Just about the only place you'll find an external I2C interface on an ordinary PC is the DDC2B bus on its VGA or DVI monitor port.

[Brumby]

Just use an off-the-shelf adapter.

I've used three different models (from China) on keyboards and barcode scanners without any problem.  For the price, you wouldn't bother messing about.

[ali6x944]

Thanx everyone I will do what u suggested guys,
Thanx very much.

[Raj]

Here-https://www.youtube.com/watch?v=UJaqHnPR-XE
Kinda overkill, you'll need Bluetooth dongle

[lapm]

I would go with off the self adapter. Saves you from many headaches...

[rch]

I would just mention my experience with a " NEWLink USB to PS/2 Keyboard & Mouse Cable".  It basically didn't work, but some random keyboard our mouse messages got through and unexpected things happened.

On the other hand I have had excellent experience with very old ps/2 mice and keyboards and a Belkin adaptor to USB.  They don't seem to sell them any more, though.