没有正确划分

问题描述

我试图将 20 除以 2，但我的 6502 计算机打印的是 254254 而不是 10。 代码如下：

PORTB = $6000
PORTA = $6001
DDRB = $6002
DDRA = $6003

E  = %10000000
RW = %01000000
RS = %00100000

N = $2000   ; 1 byte
D = $2001   ; 1 byte
Q = $2002   ; 1 byte
R = $2003   ; 1 byte

value = $0204       ; 2 bytes
mod10 = $0206       ; 2 bytes
message = $0208     ; 6 bytes

  .org $e000

error_message: .asciiz "An error occured"

loop:
  jmp loop

error:
  ldx #0
error_loop:
  lda error_message,x
  beq loop
  jsr print_char
  inx
  jmp error_loop

print_char:
  jsr lcd_wait
  sta PORTB
  lda #RS
  sta PORTA
  lda #(RS | E)
  sta PORTA
  lda #RS
  sta PORTA
  rts

lcd_wait:
  pha
  lda #%00000000 ; Set all pins on port B to input
  sta DDRB

lcd_busy:
  lda #RW        ; Set RW pin
  sta PORTA
  lda #(RW | E)  ; Set RW and E pins
  sta PORTA
  lda PORTB      ; Read port B
  and #%10000000
  bne lcd_busy

  lda #%11111111 ; Set all pins on port B to output
  sta DDRB
  pla
  rts

lcd_instruction:
  jsr lcd_wait
  sta PORTB
  lda #0         ; Clear RS/RW/E bits
  sta PORTA
  lda #E         ; Set E bit to send instruction
  sta PORTA
  lda #0         ; Clear RS/RW/E bits
  sta PORTA
  rts

divide:
  lda N
  beq error

  lda D
  beq error

  lda N
  cmp D
  bcc error

  lda #0
  sta Q

  lda N
  sta R

divloop:
  sec
  inc Q
  lda R
  sbc D
  sta R
  bcs divloop
  dec Q
  jsr print_R
  jsr print_Q
  rts

print_R:
  lda #0
  sta message

  ; Initialize value to be the number to convert
  lda R
  sta value
  lda #0
  sta value + 1
  jmp divide_int

print_Q:
  lda #0
  sta message

  ; Initialize value to be the number to convert
  lda R
  sta value
  lda #0
  sta value + 1


divide_int:
  ; Initialize the remainder to zero
  lda #0
  sta mod10
  sta mod10 + 1
  clc

  ldx #16


divloop_int:
  ; Rotate quotient and remainder
  rol value
  rol value + 1
  rol mod10
  rol mod10 + 1

  ; a,y = dividend - divisor
  sec
  lda mod10
  sbc #10
  tay   ; save low byte in Y
  lda mod10 + 1
  sbc #0
  bcc ignore_result  ; branch if dividend < divisor
  sty mod10
  sta mod10 + 1


ignore_result:
  dex
  bne divloop_int
  rol value         ; shift in the last bit of the quotient
  rol value + 1

  lda mod10
  clc
  adc #"0"
  jsr push_char

  ; if value != 0,then continue dividing
  lda value
  ora value + 1
  bne divide_int        ; branch if value not zero

  ldx #0
print:
  lda message,x
  beq return
  jsr print_char
  inx
  jmp print

push_char:
  pha  ; Push new first character onto stack
  ldy #0


char_loop:
  lda message,y    ; Get char on string and put into X
  tax
  pla
  sta message,y    ; Pull char off stack and add it to the string
  iny
  txa
  pha               ; Push char from string onto stack
  bne char_loop

  pla
  sta message,y    ; Pull the null off the stack and add to the end of the string
return:
  rts

reset:
  ldx #$ff
  txs

  lda #%11111111 ; Set all pins on port B to output
  sta DDRB
  lda #%11100000
  sta DDRA

  lda #20
  sta N
  lda #2
  sta D

  lda #%11100000 ; Set top 3 pins on port A to output
  sta DDRA
  lda #%00000001 ; Clear display
  jsr lcd_instruction
  lda #%00111000 ; Set 8-bit mode; 2-line display; 5x8 font
  jsr lcd_instruction
  lda #%00001110 ; display on; cursor on; blink off
  jsr lcd_instruction
  lda #%00000110 ; Increment and shift cursor; don't shift display
  jsr lcd_instruction


  lda #0
  sta message

  jsr divide

  jmp loop


  .org $fffc
  .word reset
  .word $0000

我希望有人看到我的错误，我已经调试了 5 个小时了。 我的 6502 的灵感来自 Ben Eater 的一款。 我使用 vasm 作为具有旧式语法的编译器。

解决方法

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