USB keyboard to PS2 adapter?

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I see USB->PS2 adapters for sale that claim to work for either USB
keyboards or USB mice. Should any adapter for one device also work for
the other, or is there something special about these?

--    St. Paul, MN

Re: USB keyboard to PS2 adapter?

Bert wrote:
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As far as I know, the "magic" is inside the keyboard or mouse itself.
The adapter is small, and passive, and there is no chip inside.

I have a mouse, which claims to be "USB/PS2" and comes with it's own
green colored passive adapter plug. The mouse itself, recognizes
the signals are coming from USB or PS/2 and adapts itself accordingly.
The fact the green passive adapter is bundled with the mouse, is
proof the mouse is a dual-protocol type design.

If your mouse doesn't come with an adapter, there is no reason to
assume it is dual-protocol. If you lost the passive adapter, then
by all means, buy another passive adapter and you can safely use it.

If you have any documentation to that effect, that the product
supports both protocols, then it would be safe to use a passive adapter.

If you have a mouse which is "USB only" internally, then slapping
a passive PS2 adapter on it would be a mistake. The mouse probably
doesn't have printed on it anywhere, that it is dual-protocol.

    "Please Note: This product is designed as a replacement adapter
     for keyboards that originally shipped with a PS/2-USB converter"

This one is along the same lines, but doesn't come with the same
warning. It should state the same warning as the other product.

This one, on the other hand, is an "active" adapter, that converts
from one protocol to another. (The "blob" in the middle of the cable,
tells me it is active.) There are no assumptions about the keyboard or mouse
in this case. But, this product is only available "in one direction".
USB host to PS2 keyboard and PS2 mouse. There is no
PS2 host to USB keyboard and/or USB mouse active adapter that
I've seen. They could make one, if they put their minds to it,
but what market would there be for it ? PS2 is disappearing from
computers as we speak. The market for that kind of active
adapter would also be disappearing. I'm really surprised that
Chesen went to the trouble of making a chip for this. (PDF inside)

You can also see the Chesen chip, on this PCI adapter board. It's
the 16 pin chip on the lower left. It converts from the USB chip
on the right, to the PS/2 keyboard and PS/2 mouse connectors on
the card faceplate. The Chesen chip is an actual processor inside,
with its own RAM and firmware.

If Chesen wanted to, they could make it work in the reverse direction
(probably a complete redesign, reusing some of the IP inside).
I'm wondering if they've made their money back on making that one
or not. The engineering to make that would not be cheap, and they
wouldn't be charging more than $5.00 for the chip. Probably a lot less.
The adapters are available at quite reasonable prices, so the profit
margins must be small.


Can a USB keyboard or mouse be damaged by usage of the passive adapter ?
I don't know the answer to that question.

Maybe someone else has tried it, and survived ? I'd have to scan the
500 page USB spec for the rest of the day, to answer that question.


Re: USB keyboard to PS2 adapter?

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Thanks for the explanation.

Oh well...

--    St. Paul, MN

Re: USB keyboard to PS2 adapter?

Bert wrote:

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Those wiring adapters only work if the device itself works to change
signalling levels when it detects the type of connection.  You cannot
use those adapters to magically convert a USB-only device into a
USB+PS/2 device.  You use those passive adapters for what is already a
USB+PS/2 device - or you get an active adapter that converts the

Re: USB keyboard to PS2 adapter?

On 11/10/2011 10:23 AM, VanguardLH wrote:
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You you seen an active adapter, that will allow any USB mouse and
keyboard to be plugged into PS/2 ports, for sale?  I looked for such an
animal, and could not find one.

Re: USB keyboard to PS2 adapter?

Grinder wrote:

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These are sold as *replacement* adapters.  You have a USB+PS/2 keyboard
or mouse but have lost the adapter.  For example, you hooked them up to
a USB port, stowed the adapters in a drawer years ago, now you need PS/2
connectivity (on an old host whose BIOS doesn't itself support USB input
devices), but can't find those adapters anymore.

This is an active adapter that will convert the signalling between USB
to PS/2.  Pricey at $80.  I've also heard of but not investigated the
use of a KVM to do the conversion; i.e., you plug a USB-only keyboard
into the input USB port of the KVM and use its PS/2 output to the chost.
I suspect a KVM that does conversion would be more expensive than a KVM
that simply does electronic switching.

It would be far cheaper to buy a USB+PS/2 or PS/2-only keyboard to
replace or augment your USB-only keyboard if and when you need PS/2
connectivity for an older BIOS (or you don't want high bandwidth use
over a *shared* USB controller to afflict your keyboarding or mousing

This goes the other way (PS/2 to USB) and are far cheaper.  There are
few USB-to-PS/2 active converters available and they seem pricey.
Apparently it is easy and cheap to convert between connection protocols
when going from PS/2 to USB than it is to go from USB to PS/2.  Get a
USB+PS/2 or PS/2 keyboard for a less costly and more reliable setup
rather than have dongle crap sticking out the backside of your computer.

Re: USB keyboard to PS2 adapter?

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I've bought a couple of these to work the other way around and they worked
fine. But you do have to make sure and get the keyboard to purple and the
mouse to green. As a matter of fact, the keyboard I'm using right now is
hooked up through one of these. =

            -- I'm out of white ink --

Re: USB keyboard to PS2 adapter?

Menno Hershberger wrote:

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Bert said he wanted to go USB->PS/2.  That's what Grinder said he was
looking for, too.  Your suggestion won't work since it goes PS/2->USB.

That adapter you suggested goes the wrong way for what Bert and Grinder
asked for.  You showed an adapter that goes from PS/2 to USB.  Look at
the connectors, especially the USB end.  If the user already has a USB
keyboard and a USB mouse, they don't need that converter since it is
used to connect to a USB port.  The USB keyboard they have can
obviously plug into a USB port without the use of that adapter.

Bert wrote that he wanted to go USB to PS/2 (not the other way around
using the adapter you showed).  That means a *female* USB connector
(not the male USB connector in your adapter) into which the USB
keyboard or USB mouse would insert.  To connect a USB keyboard to a
PS/2 port means the male USB plug goes into a female USB jack which
then goes to male PS/2 plugs to go into the female PS/2 ports.  Your
suggestion for an adapter has the wrong gender connectors.

The one you showed going PS/2 to USB are plenty and cheap.  Going the
other way from USB to PS/2 takes an *ACTIVE* converter which makes it
pricey so that getting a USB+PS/2 or PS/2 device to connect directly to
the PS/2 ports would be a cheaper solution instead of using an active

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