Strange behaviour with both shift-keys pressed

[traumatic]

Did you know that some characters don't work when both shift keys are pressed on your keyboard?

Try to write the following with both shift-keys down:

THE QUICK BROWN FOX JUMPS OVER THE LAZY DOGS BACK

My result:

HE QUIC BROWN OX UMP OVER HE Y OG BC

Does anyone know why? Is this some kind of controller limitation or some windows tasks running in the background?

[zikitrake]

My result is ok

THE QUICK BROWN FOX JUMPS OVER THE LAZY DOGS BACK

[DarkDragon]

You don't have an internal speaker, right? Otherwise it would go crazy if you hold shiftl+shiftr+t. Its a hardware limitation of your keyboard (It's on 90% of all keyboards, but sometimes with different keys). There are also some other combinations which don't work (Just try it out: press all keys down with your hand and it won't write anything anymore [a-s-x-c for example]).

[ts-soft]

THE QUICK BROWN FO JUMPS OVER THE LAZY DOGS BACK

X doesn't work on MS Keyboard with doubleshift

[Trond]

It's because of the wireing inside the keyboard.

[traumatic]

It's because of the wireing inside the keyboard.

Do you happen to have some more in-depth information on this? Thank you!

[djes]

I had this problem in a game using several keys (for two players). If you define an action on each shift keys, sometimes they're not detected, or the others keys! Annoying! A solution is for the player 1 to use the shift key, and the other with CTRL.
In fact, there's this problem if you're using the same row of keys.

[blueznl]

MS Natural Keybaord:

TE UIC RWN JUS VER TE LAY DG

HP laptop keyboard:

THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG

[Trond]

5 year old Packard Bell laptop keyboard:
THEQUIKROWFOJUPSOERTHELAYDOG

JAKDAWSLOESYIGSPHIOFQUART
(Jackdaws loves my big sphinx of quartz)

Is this the first where the space key doesn't work?

Here is more information (I didn't read it): http://www.dribin.org/dave/keyboard/one_html/

[traumatic]

Great, thanks Trond!

[blueznl]

Now we get countless experiments on incompatible keyboards A new PureBasic FAD (TM) has been born!

[Kaeru Gaman]

I'd like to try an explanation why this behaviour occurs.

the keys pressed have to be encoded some way to be sent via the port where the keyboard communicated with the mainboard.
this port has a limited width.

to encode a keyboard with over 100 keys in a way that each keypress can occur at the same time,
the port needs a width of 128bit (1bit for every key)

when the port is narrower, the keypresses have to be encoded in a way that some combinations cannot be encoded correctly.
since in no normal cases one would use both shift-keys at the same time, this is a combination you can easily leave out.

hope that explanation is correct enough, I know the problem for a long time, but I never read long essays about it.

[Demivec]

My Logitech keyboard's pathetic performance:

H UICK BON FOX JUMPS OV H LAZ DOGS BACK

[Derek]

My HP laptop gives a perfect result whereas my logitech is just as bad as Demivec's.

[Kaeru Gaman]

I bet, a Laptop has a broader Port than an attached Keyboard via USB or PS2....