keyboards

  • Thread starter Thread starter doubleukay
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doubleukay

hi NG,

just wondering, why are some keyboards able to have more keys pressed
simultaneously?
 
doubleukay said:
hi NG,

just wondering, why are some keyboards able to have more keys pressed
simultaneously?
Click to expand...


It depends on the technology used for working out which keys are pressed.

You can have each key with it's own switch, which allows multiple keys
simultaneously but requires lots of I/O.

You can reduce your I/O overhead by organising the keys into rows and
columns with a contact that connects the intersection together. With a
clever method of scanning rows, then columns you can work out which key was
pressed... but only one at a time. Two keys pressed on different rows and
columns produces four possible combinations... you can't tell out of the
four, which two have been pressed. Keyboards of this type are obviously
cheaper to produce and all but a handful of keyboards are likeely to be this
type.

Ben
 
Ben said:
It depends on the technology used for working out which keys are
pressed. You can have each key with it's own switch, which allows
multiple keys simultaneously but requires lots of I/O.

You can reduce your I/O overhead by organising the keys into rows
and columns with a contact that connects the intersection together.
With a clever method of scanning rows, then columns you can work
out which key was pressed... but only one at a time. Two keys
pressed on different rows and columns produces four possible
combinations... you can't tell out of the four, which two have
been pressed. Keyboards of this type are obviously cheaper to
produce and all but a handful of keyboards are likeely to be this
type.
Click to expand...

For simple circuits that is true. However a few years ago various
networked schemes were published right in comp.arch.embedded, I
believe, allowing for various discrete multi key detection levels.

Of course the simple answer for the OP is: They all allow multiple
key depression. Your cat does it all the time. :-) (Exception -
the ASR33 teletype machines lock out all other keys when one other
than shift or control is down)
 
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