GPBX
         PLA
         STA   RETADR
         PLA
         STA   RETADR+1
         PLA
         STA   ADDR1      ; ZERO PAGE
         PLA
         STA   ADDR1+1
         LDA   ERRCTRL
         CMP   #1
         BEQ   :CHKERR
         JMP   :ERREND
:CHKERR
         LDA   ADDR1+1
         CMP   #$C0       ; MAX COL + 1
         BNE   :BADHI
         LDA   ADDR1
         CMP   #$64
         BCS   :BADLO
         LDA   ADDR1
         CMP   #$60
         BCC   :BADLO
         JMP   :ERREND
:BADHI
         _ERR  :E_SID;:E_BHI;:E_DMP1;RETURN;#10
         JMP   :ERREND
:BADLO
         _ERR  :E_SID;:E_BLO;:E_DMP1;RETURN;#10
:ERREND
         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
         LDA   RETADR+1
         PHA
         LDA   RETADR
         PHA
         TYA              ; BTN FLAG MOVE TO A
         RTS
:E_SID   ASC   "GPBX (PBX MACRO)",00
:E_DMP1  ASC   "DUMPING RETURN BLOCK...",00
:E_BHI   ASC   "BAD HIGH BYTE--NOT A PADDLE BUTTON!.",00
:E_BLO   ASC   "BAD LOW BYTE--NOT A PADDLE BUTTON",00