163 lines
3.0 KiB
ArmAsm
163 lines
3.0 KiB
ArmAsm
PORTB = $6000
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PORTA = $6001
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DDRB = $6002
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DDRA = $6003
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value = $0200 ; 2 bytes
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mod10 = $0202 ; 2 bytes
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message = $0204 ; 6 bytes
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E = %10000000
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RW = %01000000
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RS = %00100000
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.org $8000
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reset:
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lda #%11111111 ; set all pins on port B to output
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sta DDRB
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lda #%11100000 ; set top 3 pins on port A to output
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sta DDRA
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lda #%00111000 ; set 8-bit mode, 2 line display, 5x8 font.
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jsr command_to_lcd
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lda #%00001110 ; set display and curson on, do not blink
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jsr command_to_lcd
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lda #%00000110 ; set entry mode increment and display shift off
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jsr command_to_lcd
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lda #%00000001
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jsr command_to_lcd
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; null terminated string init
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lda #0
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sta message
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; initialise value to number to be converted
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lda number
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sta value
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lda number + 1
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sta value + 1
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divide:
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; initialise mod10 to be zero
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lda #0
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sta mod10
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sta mod10 + 1
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clc ; clear carry
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ldx #16
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divloop:
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; rotating the qotient and remainder
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rol value
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rol value + 1
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rol mod10
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rol mod10 + 1
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; a,y = dividend - divisor
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sec
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lda mod10
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sbc #10
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tay ; save low byte to Y
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lda mod10 + 1
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sbc #0
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bcc ignore_result ; branch if dividend < divisor
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; store result
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sty mod10
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sta mod10 + 1
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ignore_result:
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dex
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bne divloop
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rol value ; shift in the last bit of the quotient
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rol value + 1
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lda mod10
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clc
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adc #"0"
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jsr push_char_message
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; if value != 0, continue dividing
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lda value
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ora value + 1
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bne divide ; branche if value isn't 0
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; once we are done dividing, print message.
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ldx #0
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print:
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lda message,x
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beq loop ; load sets zero flag (checked by beq) when it loads a zero byte.
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jsr ASCII_to_lcd
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inx
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jmp print
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loop:
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jmp loop
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number: .word 1729
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push_char_message:
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pha ; push char to stack
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ldy #0
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char_loop:
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lda message,y ; get char on string into x
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tax
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pla
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sta message,y ; add char from from stack to string
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iny
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txa ; put char in x into a
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pha ; put char onto stack, if 0 zero flag set
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bne char_loop
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pla
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sta message,y ; put null back onto end of string
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rts ; RETURN
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lcd_wait:
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pha ; save porta to stack
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lda #%00000000 ; set PORTB to input
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sta DDRB
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lcdbusy:
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lda #RW
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sta PORTA
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lda #(RW | E)
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sta PORTA
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lda PORTB
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and #%10000000 ; check LCD busy flag
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bne lcdbusy ; branch if it is NOT set
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lda #RW
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sta PORTA
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lda #%11111111 ; set PORTB to output again
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sta DDRB
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pla ; load stack value back to porta
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rts ; RETURN
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command_to_lcd:
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jsr lcd_wait ; ensure LCD is not busy before sending instruction
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sta PORTB
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lda #0 ; clear RS/RW/E bits
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sta PORTA
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lda #E ; set enable bit to send instruction
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sta PORTA
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lda #0 ; clear RS/RW/E bits
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sta PORTA
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rts ; RETURN
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char_to_lcd:
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jsr lcd_wait ; ensure LCD is not busy before sending instruction
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sta PORTB
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lda #RS ; RS set
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sta PORTA
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lda #(RS | E) ; RS and E set
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sta PORTA
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lda #RS ; RS set
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sta PORTA
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rts ; RETURN
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.org $fffc
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.word reset
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.word $0000
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