Hi Dave,

the question is, is there any advantage on wasting an interrupt pin and many additional hardware ?

The answer is No.

How you say, nobody can press a key with 1Mhz, but interrupts only useful to handle very fast events. And a keyboard should read no faster than 10ms to perform debouncing.
Also often not only key pressing was needed. You want also to see, if a shift key was pressed or repeat a key code periodically after some time of pressing. So typically keyboard routines debounce the key and signal any key pressing and also any key releasing event.
On a matrix also 2 keys can be pressed and identified.
If you read a keyboard every 10,000 cycle and need 100 cycle for it, this give a CPU load of only 1%, which is very small in most cases.

So the interrupt approach should only be useful on a single key and with very high importance, e.g. for an emergency break key.


Peter