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STOP

     Purpose:  Check if <STOP> key is pressed
Call address:  $FFE1 (hex)  65505 (decimal)
Communication registers:  A
Preparatory routines:  None
Error returns:  None
Stack requirements:  None
Registers affected:  A, X

Description:

If the <STOP> key on the keyboard was pressed during a UDTIM call, this call returns the Z flag set. In addition, the channels will be reset to default values. All other flags remain unchanged. If the <STOP> key is not pressed then the accumulator will contain a byte representing the lost row of the keyboard scan. The user can also check for certain other keys this way.

How to Use:

  1. UDTIM should be called before this routine.
  2. Call this routine.
  3. Test for the zero flag.

EXAMPLE:

    JSR UDTIM   ;SCAN FOR STOP
    JSR STOP
    BNE *+5     ;KEY NOT DOWN
    JMP READY   ;=... STOP
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