使用Zero Page Indirect Addressing的6502内存循环程序无法正常运行，请求故障排查

Let's walk through the issues in your code and get it working correctly:

Key Issues in Your Original Code #

1. Unclear Carry Flag During 16-Bit Addition #

This is the critical bug breaking your program. When you perform the 16-bit increment of your zero-page pointer:

LDA $00 
ADC #1 
STA $00 
LDA $01 
ADC #0 
STA $01 

you only clear the carry flag once at the start of the program. If the low byte ($00) ever rolls over from $FF to $00, the ADC #1 will set the carry flag to 1. This carry stays set for the next iteration of the loop, so the next ADC #1 will add 1 plus the carry to $00, making your pointer jump two bytes instead of one. Over time, this causes your writes to skip addresses and fill memory incorrectly.

2. Overcomplicated Pointer Management #

You’re manually incrementing a 16-bit pointer when you don’t need to. Since you’re filling a contiguous 128-byte block, you can use the Y register as an index—its 8-bit range (0-127) perfectly fits your needs. This simplifies the code and eliminates the risk of 16-bit addition errors.

3. Missing BASIC Loader (For Commodore 64) #

If you’re running this on a Commodore 64 (the most common system for $8001-originated code), starting at *=$8001 without a BASIC header will cause the interpreter to treat your machine code as invalid BASIC tokens. You need a small header to let BASIC call your program.

Fixed Code (Simplified Version) #

This version uses the Y register for indexing, which is cleaner and more reliable:

*=$8001
; BASIC loader: 10 SYS 2064 (2064 = $810)
.byte $0C,$08,$0A,$00,$9E,$20,$32,$30,$36,$34,$00,$00,$00

*=$810 ; Actual program start
; Initialize zero-page pointer to $0400
LDA #$00
STA $00
LDA #$04
STA $01

CLD ; Disable decimal mode (critical for binary arithmetic)

LDX #128 ; Loop counter: 128 iterations
LDY #0   ; Index starts at 0
loop:
LDA #$01 ; Value to store
STA ($00),Y ; Store at pointer + Y index

INY ; Increment index for next address

DEX ; Decrement loop counter
BNE loop ; Repeat until counter hits 0

RTS ; Return to caller

Fixed Code (Original Pointer Approach) #

If you prefer to keep the manual 16-bit pointer increment, just add a CLC before each addition to clear the carry flag:

*=$8001
; BASIC loader: 10 SYS 2064
.byte $0C,$08,$0A,$00,$9E,$20,$32,$30,$36,$34,$00,$00,$00

*=$810
LDA #$00
STA $00
LDA #$04
STA $01

CLD ; Disable decimal mode

LDX #128
LDY #0
loop:
LDA #$01
STA ($00),Y

; Fix: Clear carry before 16-bit addition
CLC
LDA $00
ADC #1
STA $00
LDA $01
ADC #0
STA $01

DEX
BNE loop

RTS

How to Test #

If you’re using a C64 emulator like VICE:

1. Load the code into memory
2. Type RUN (or SYS 2064) to execute the program
3. Check memory from $0400 to $047F—you’ll see all bytes set to $01

内容的提问来源于stack exchange，提问作者M. Gianota