APPENDIX TWELVE



     DEST    EQU     SOURCE+2
     START   EQU     $0600           ;START address
     OSROM   EQU     $C000           ;address of OS ROM start
     OSRAM   EQU     $4000           ;address of ROM
                                     destination
     NMIEN   EQU     $D40E           ;NMI enable register
     PORTB   EQU     $D301           ;memory mgt control
                                     latch
             ORG     START
             LDA     #low OSROM
             STA     SOURCE
             STA     DEST            ;initialize copy addrs
             LDA     #high OSROM
             STA     SOURCE+1
             LDA     #high OSRAM
             STA     DEST+l
             LDY     #0
                                     ;Repeat
     Pass1   LDA     (SOURCE),Y      ;copy ROM to RAM
             STA     (DEST),Y
             INY
             BNE     Pass1 
             INC     DEST+1
             INC     SOURCE+1
             BEQ     Swap            ;If done
             LDA     SOURCE+l
             CMP     #$D0
             BNE     Pass1           ;skip 2K block at $D000
             LDA     #$D8
             STA     SOURCE+1
             BNE     Pass1           ;Until SOURCE = $0000
     Swap    PHP                     ;save processor status
             SEI                     ;disable IRQs
             LDA     NMIEN
             PHA                     ;save NMIEN
             LDA     #0
             STA     NMIEN           ;disable NMIs
             LDA     PORTB
             AND     #$FE            ;turn off ROMs
             STA     PORTB           ;(leaving BASIC
                                     unchanged!)
             LDA     #high OSROM
             STA     DEST+1          ;set up block copy
             LDA     #high OSRAM
             STA     SOURCE+1
                                     ;Repeat