| ??? 01/31/08 09:01 Modified: 01/31/08 09:03 Read: times |
#150104 - debouncing Responding to: ???'s previous message |
Andy Neil said:
Yes, there was an 8051 in the original PC keyboard. Ah, I believe that; all what I said was that I doubt there was any intel microcontroller in the original AT keyboard (which is a completely different animal than the original PC keyboard). Andy Neil said:
After all, what comes out of a PC keyboard is a serial data protocol - so the keyboard's "processor" would have to do the debouncing before it could send the appropriate protocol messages for "key-down" and "key-up"... Yes, as I said above, the chip inside the keyboard undoubtedly performs debouncing of the "switches" in the matrix. However, you are bringing in open collector signals with mostly unknown pullup resistance into your box through some one-two metres (UK/US: 3'-6' :-) ) long cable, via a potentially noisy environment. Would you leave the success of receiving data via such connection to a single sample of the data line in an interrupt triggered directly by the clock line? As it has been said here many many times: tried, works. Now it's time for Erik's sermon. :-) JW |
