0 x = peek(53281)
20 x = x + 1
30 y = x
40 x = y + 1
50 a = y
60 x = x - 1
70 poke 53280, x
80 poke 53281, a
90 end
```

.C:c000  AE 21 D0    LDX $D021   //// ex. x=05
.C:c003  E8          INX         ///// x=06
.C:c004  8E 20 C0    STX $C020   /// $c020 = 06
.C:c007  AC 20 C0    LDY $C020   //// Y= 06
.C:c00a  C8          INY         //// Y=07
.C:c00b  8C 20 C0    STY $C020   ///  $c020 = 07
.C:c00e  AE 20 C0    LDX $C020   /// X= 07
.C:c011  AD 20 C0    LDA $C020   ///  A=07
.C:c014  CA          DEX         /// X=05
.C:c015  8E 20 D0    STX $D020   /// $d020 = 05
.C:c018  8D 21 D0    STA $D021   /// $D021 = 07
.C:c01b  60          RTS
.C:c01c  00          BRK
.C:c01d  00          BRK
.C:c01e  00          BRK
.C:c01f  00          BRK
.C:c020  F8          SED