*
*``````````````````````````````*
* GPBX :: GET PADDLE BUTTON X  *
*                              *
* GETS STATE OF PADDLE BUTTON  *
* SPECIFIED AND RET 0, 1 IN A  *
*-                            -*
* CLOBBERS:                    *
*                              *
* FLAGS:  ???-----  REG: A-YM  *
*-                            -*
* CYCLES: ???                  *
* SIZE:                        *
*-                            -*
* USAGE:                       *
*        LDA   #>(ADDRESS)     *
*        PHA                   *
*        LDA   #<(ADDRESS)     *
*        PHA                   *
*        JSR   GPBX            *
*                              *
* --- WHERE:                   *
*                              *
*    BUTTON 0 = $C061 (PB0)    *
*    BUTTON 1 = $CO62 (PB1)    *
*    BUTTON 2 - $C063 (PB2)    *
*    BUTTON 3 = $C060 (PB3)    *
*-                            -*
* ENTRY                        *
*                              *
* TOP OF STACK                 *
*                              *
* LOW BYTE OF RETURN ADDRESS   *
* HI BYTE OF RETURN ADDRESS    *
* LOW BYTE OF PDL BTN ADDRESS  *
* HI BYTE OF PDL BTN ADDRESS   *
*-                            -*
* EXIT                         *
*                              *
* TOP OF STACK                 *
*                              *
* LOW BYTE OF RETURN ADDRESS   *
* HI BYTE OF RETURN ADDRESS    *
*                              *
*   A = 1 IF PRESSED, 0 IF NOT *
*   X = UNCHANGED              *
*   Y = GARBAGE                *
*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
*
* CHANGE THIS LATER TO ACCEPT ALL BUTTONS, 0-4
*
GBPX
*
** SAVE RETURN ADDRESS
*
                                PLA
                                STA   :RETADR
                                PLA
                                STA   :RETADR+1
*
** GET PARAMETER
*
                                PLA
                                STA   ADDR1      ; ZERO PAGE
                                PLA
                                STA   ADDR1+1
*
*
                                LDY   #$00
                                LDA   (ADDR1),Y  ; IF BTN = PUSHED
                                BMI   :1
                                JMP   :0
:1
                                LDY   #$01       ; BTN PUSHED;A=1
                                JMP   :EXIT
:0
                                LDY   #$00       ; BTN NOT PUSHED;A=0
*
:EXIT
*
** RESTORE RETURN ADDRESS
*
                                LDA   :RETADR+1
                                PHA
                                LDA   :RETADR
                                PHA
*
                                TYA              ; BTN FLAG MOVE TO A
                                RTS
*
** DATA
*
:RETADR        DS            2
*