NOTE: The following is helpful guide and is NOT part of the puzzle.

The first digits are decimal (as presented in the puzzle); 0x and 0y are representation of hex values

24:         CLC - clear carry flag
30,0x,0y:   ASL \$0y0x,X - bitwise shift memory location (\$0y0x + .X) left;
put the left most bit into the carry flag
32,210,255: JSR \$FFD2 - output the character whose value is in register A
96:         RTS - equivalent of end
121,0x,0y:  ADC \$0y0x,Y - add with carry the value of memory location
(\$0y0x + .Y) to register A
144,0x:     BCC (offset) - branch #\$0x signed bytes from the end of this
instruction if the carry is clear (ie. carry == 0)
152:        TYA - copy the value of register Y to register A
153,0x,0y:  STA \$0y0x,Y - store register A in memeory location (\$0y0x + .Y)
160,0x:     LDY #\$0x - load register Y with the value #\$0x
162,0x:     LDX #\$0x - load register X with the value #\$0x
169,0x:     LDA #\$0x - load register A with the value #\$0x
185,0x,0y:  LDA \$0y0x,Y - load register A with the value of memory location (\$0y0x + .Y)
192,0x:     CPY #\$0x - compare the value of register Y with #\$0x
200:        INY - increase register Y by 1
208,0x:     BNE (offset) - if last compare is not equal, branch #\$0x signed
bytes from the end of this instruction
224,0x:     CPX #\$0x - compare the value of register X with #\$0x
232:        INX - increase register X by 1