174 lines
2.5 KiB
ArmAsm
174 lines
2.5 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 send_inst
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lda #%00001110 ; Display on; cursor on; blink off
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jsr send_inst
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lda #%00000001 ; Reset display
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jsr send_inst
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lda #%00000110 ; Increment and shift cursor; don't shift display
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jsr send_inst
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;; division rotate minus
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lda #0
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sta message
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;; initialize value to the conversion number
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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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;; initialse remainder to 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
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ldx #16
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divloop:
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;; rotate the quotient
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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 in Y
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lda mod10 + 1
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sbc #0
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bcc ignore_result ; branch if dividend < divosr
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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 last bit of 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
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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
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ldx #0
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print:
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lda message,x
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beq loop
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jsr send_data
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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 65521
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;; add character in A to start of message
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push_char:
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pha ; Push first char on stack
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ldy #0
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char_loop:
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lda message,y ; get char on string and put in X
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tax
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pla
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sta message,y ; pull char off stack and add it to the string
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iny
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txa
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pha ; put char from string and put it back
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bne char_loop
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pla
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sta message,y ; Pull null off stack stuff on end of string
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rts
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lcd_wait:
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pha
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lda #%00000000 ; PORT B to INPUT
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sta DDRB
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lcd_busy:
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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
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bne lcd_busy
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lda #RW
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sta PORTA
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lda #%11111111 ; PORT B to output
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sta DDRB
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pla
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rts
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send_inst:
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jsr lcd_wait
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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 E 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
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send_data:
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jsr lcd_wait
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sta PORTB
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lda #RS ; Set RS; Clear RW/E bits
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sta PORTA
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lda #(RS | E) ; Set E bit to send instruction
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sta PORTA
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lda #RS ; Clear E bits
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sta PORTA
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rts
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.org $fffc
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.word reset
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.word $0000
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