if read1($00FFD5) == $23
    sa1rom
    !addr = $6000
    !bank = $000000
else
    lorom
    !addr = $0000
    !bank = $800000
endif

org $00FFE6|!bank
    dw $F9F5

org $00F9F5|!bank
    LDA #$FF
    STA $0100|!addr
    LDA #$0F
-   STA $2100
    EOR #$0F
    LDX $0100|!addr
    BMI -
    RTI