Re: Are all PS/2 to USB splitter adapters bad for old PS/2 keyboards?

Ant <[email protected]> wrote:

> Hello,
> 
> Are all PS/2 to USB splitter adapters bad for old PS/2 keyboards? I have 
> two different brands PS/2 to USB splitter adapters for my old PS/2 
> keyboards & mouses for two different old home built PCs (updated Windows 
> 10 Pro. and Linux/Debian trixie stable [even in its text mode]). I 
> didn't want to buy new mouses and keyboards since I have many old ones 
> to use. I'm a fast typist on clicky keyboards, but I noticed results are 
> not fast and good. When I hold a letter/number down and then press a 
> Shift or Caps Lock key to show its opposite, the repeating results just 
> stop showing (nothing show anymore). This is annoying when gaming like 
> when I use W to move forward and want to use shift key. When I type 
> fast, I get incorrect, missing, or duplicate characters.
> 
> It's very annoying! PS/2 mouses are fine though! Are splitters not good 
> and I have to get USB PC104 keyboards? :( Thank you for reading and 
> hopefully answering soon. :)

If you are trying to connect a USB-only device to a PS/2 port, the
hardware protocols do not match.  You either have to get devices that
state they support both PS/2 and USB (they support both hardware
protocols), or you need to get an active USB-to-PS2 cable which has
inbuilt logic to convert between the hardware protocols.  Passive cables
do nothing for hardware protocol conversion.

It's been a very long time since I looked at active USB-to-PS2 converter
cables.  Back then you could still buy keyboards and mice that stated
they supported both USB and PS2.  Nowadays finding those is tough as all
manufacturers went to USB.

Used to be the USB-to-PS2 converters were bulky boxes inline with the
cables.  Nowadays they look like a splitter cable with a bulge inline
for the logic.  From your description, you are trying to use PS/2
keyboards and PS/2 mice to connect to a USB port.  You can find them for
not much money at various online stores, like:

https://www.newegg.com/p/pl?d=active+usb+to+ps2+converter

You need an active converter in the splitter adapter to do the logic in
converting from PS/2 hardware protocol to the USB hardware protocol.
They are not compatible without conversion.  Simply rewiring the pinouts
won't work as that does nothing to convert between hardware protocols.

I take it you have no space USB port in the system case to which you
could connect USB-only keyboards or USB-only mice.  PS/2 is interrupt
driven: the interrupt gets stacked, and quickly addressed.  USB is a
polled protocol.  It a poll is missed on a mouse or keyboard event, it
won't be until the next poll when the event is recognized.  That's why
some gamer systems still come with PS/2 backpanel ports on the mobo.
Also, N-key rollover (how many keys you can concurrently press, and have
all of them recognized) is higher with PS/2 devices.  USB devices have
small N-key rollover although they eventually upped the count.  Used to
be if you used one hand for 4 concurrent keypresses, and the other hand
for another 4 concurrent keypresses that some were unrecognized with USB
keyboards, but were all recognized for PS/2 keyboard.  Besides hunting
for USB-attached keyboards and mice that note they support both PS/2 and
USB for which you could use passive USB-to-PS2 cables or splitters, you
need to check the N-key rollover specified for the keyboards.  

The latest mechanical keyboard I got (Logitech K845) supports N-key
rollover, but Logitech no longer specifies the number of concurrent
keypresses.  I think it is 8 or 10.  For word processing, you rarely go
beyond 4-key rollover, but for games you could exceed that with both
hands using multiple fingers for several concurrent key combos, like
crabbing to the left while angling forward while hitting a fire button
while crouching and in sneak speed.

N-key rollover means all the keys can be concurrently pressed on the
keyboard, and all keys are recognized.  Well, I don't remember any
keyboard having 104-key rollover.  They typically had about 10-key
rollover.  After all, with 10 fingers, that's the limit of how many keys
you can concurrent press.  Well, you could smash you hand onto the
keyboard, but you wouldn't know what keypresses you activated.  USB
keyboard didn't have rollover, but most nowadays should have 6-key as
that is the limit for the USB polling hardware protocol.  To get more
than 6-key rollover means the keyboard has to pretend to be a USB hub
with multiple keyboards connected.  The 6-key limit is a subset of the
HIT protocol (boot protocol) meant for simplified use, like when in the
BIOS config screens.  There is a more featured report protocol that
allows some arbitrary number of keys at once, but I never bothered to
investigate that.  I don't have fast-paced adrenalin pumping
shoot-everything video games.  Never had a problem with the 1 to 4 key
rollover of a USB keyboard to a USB port when playing stealth games.

https://www.devever.net/~hl/usbnkro