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SCNKEY

     Purpose:  Scan the keyboard
Call address:  $FF9F (hex)  65439 (decimal)
Communication registers:  None
Preparatory routines:  IOINIT
Error returns:  None
Stack requirements:  5
Registers affected:  A, X, Y

Description:

This routine scans the Commodore 64 keyboard and checks for pressed keys. It is the same routine called by the interrupt handler. If a key is down, its ASCII value is placed in the keyboard queue. This routine is called only if the normal IRQ interrupt is bypassed.

How to Use:

  1. Call this routine.

EXAMPLE:

  GET  JSR SCNKEY      ;SCAN KEYBOARD
       JSR GETIN       ;GET CHARACTER
       CMP #0          ;IS IT NULL?
       BEQ GET         ;YES... SCAN AGAIN
       JSR CHROUT      ;PRINT IT
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