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Example showing how to create a DOS 3.3 binary header and program that is automatically loaded into the desired ORIGIN memory address.
113 lines
2.8 KiB
Plaintext
113 lines
2.8 KiB
Plaintext
; --------------------------------------------------
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; Example showing how to create a DOS 3.3 binary
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; header and program that is automatically loaded
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; into the desired ORIGIN memory address.
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; --------------------------------------------------
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processor 6502
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; --------------------------------------------------
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; Desired origin
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; - Origin must be less than $C000
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; - Origin + size must be less than $13000
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; - Origin must be $0803 or aligned to $xx00
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; --------------------------------------------------
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ORIGIN equ $2000
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SIZE equ END_OF_PRORGAM-ORIGIN
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; --------------------------------------------------
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; DOS 3.3 binary header (4 bytes)
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; --------------------------------------------------
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org ORIGIN - 4 ; Subtract 4 ensures correct memory locations
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word ORIGIN ; Origin (2 bytes)
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word SIZE ; Size (2 bytes), must be length - 4
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; --------------------------------------------------
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; ROM routines
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; --------------------------------------------------
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HOME equ $FC58
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; --------------------------------------------------
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; Origin and start of program
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; --------------------------------------------------
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org ORIGIN ; Starting address
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start
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; --------------------------------------------------
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; Clear screen
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; --------------------------------------------------
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jsr HOME
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; --------------------------------------------------
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; Print "START $" (7 chars) to $0400..$0406
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; --------------------------------------------------
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ldx #0
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pfx_loop
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lda prefix,x
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ora #$80
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sta $0400,x
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inx
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cpx #7
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bne pfx_loop
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; --------------------------------------------------
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; Print origin in hex to $0407 - $040A
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; --------------------------------------------------
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; High byte high nibble
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lda #>start
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lsr
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lsr
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lsr
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lsr
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tax
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lda hexchar,x
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ora #$80
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sta $0407
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; High byte low nibble
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lda #>start
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and #$0F
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tax
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lda hexchar,x
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ora #$80
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sta $0408
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; Low byte high nibble
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lda #<start
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lsr
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lsr
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lsr
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lsr
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tax
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lda hexchar,x
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ora #$80
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sta $0409
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; Low byte low nibble
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lda #<start
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and #$0F
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tax
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lda hexchar,x
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ora #$80
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sta $040A
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; --------------------------------------------------
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; Endless loop (text stays on screen)
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; --------------------------------------------------
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done jmp done
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; --------------------------------------------------
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; Data
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; --------------------------------------------------
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prefix
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byte "START $"
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hexchar
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byte "0123456789ABCDEF"
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END_OF_PRORGAM ; Don't add instructions after this line
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