The processor polls U2 to get the current configuration of the
switches.
Pin 1 of U2 is pulled low which then loads the state of D0 thru D7
(/BANK1 and /BANK2 select which switches to read), The serial data is
then read from U2 via pin 9 by the control board MCU, U6.
On Sat, 20 Aug 2005 12:47:14 -0700 (PDT),
[hidden email] wrote:
>Good day all!
> I was trying to understand how the keyboard signaled the controller
>processor that a new key was punched but to no avail. Also, the shift
>reg. (U2) notes which keys are pushed but I can't see how this works. The
>inputs of U2 are pulled up with external 100k r's but the input of U2
>being a 'hc device loads the input circuitry very very little and so the
>input would never go to a low logic level.
> I take it that until the processor is some how notified that a key is
>pushed, it remains in sleep mode. Hard for me to understand without some
>help but I'm sure, you guys have the answers.
> Thanks for any encouragement, Bob K7HBG
>
>
>
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