Echo = $FFEF
KbdRdy = $D011
Kbd = $D010

Begin:
    JSR GetChar     ;  Read character from keyboard and store in accumulator
    JSR Echo        ;  Echo value in accumulator  to screen
    JMP Begin       ;  Loop forever
    
GetChar:
    LDA KbdRdy      ;  Key ready?
    BPL GetChar     ;  Loop until ready
    LDA Kbd         ;  Load character
    RTS             ;  Return
