82 lines
1.3 KiB
ArmAsm
Executable file
82 lines
1.3 KiB
ArmAsm
Executable file
;;Screen print. Draws a pixel at a specified position.
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.proc pixel_draw; Draws a pixel at [Y = FB , X = FC, FD]. Y = 0 - 320, X= 0 - 200
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;;write_byte = 00010000,
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LDA $FC ; X (mod 8)
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AND #%00000111
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;;Store pixel in byte
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TAX
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LDA #%10000000
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INX
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tt:
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DEX
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BEQ end__;Y=0 end this
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CLC
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ROR A
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jmp tt
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end__:
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STA $FE
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;;FIND THE POSITION IN MEMORY TO WRITE PIXEL
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;; + + + + + > X
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;; +
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;; +
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;;\/
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;; Y
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;;
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;; Let be this position in memory be stored in [$49, $4A] temporaraly
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;;pos = x_offset
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LDA #%11111000
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AND $FC
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STA $49
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LDA $FD
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STA $4A
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;;y_offset because chuncks aka y_offset_bc
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LDA #%00000111 ; A = y (mod 8)
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AND $FB
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;;pos += y_offset_bc
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CLC
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ADC $49
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STA $49
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LDA #$00
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ADC $4A
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STA $4A
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LDY $FB
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LDA #$00
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STA $4B
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;;y =8 translates to 320 bytes.
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LDA #%11111000 ; A = y - [y (mod 8)]
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AND $FB
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STA $FB
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;;We need to A = A*40 =A * 2^3 * 5
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;;A = A*2^3
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mult_16 $FB, $4B
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mult_16 $FB, $4B
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mult_16 $FB, $4B
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;;*5
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Add_16 $49, $4A, $FB, $4B
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Add_16 $49, $4A, $FB, $4B
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Add_16 $49, $4A, $FB, $4B
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Add_16 $49, $4A, $FB, $4B
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Add_16 $49, $4A, $FB, $4B
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STY $FB
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;;add offset for where bitmap is
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Add_16 $49, $4A, #<Bitmap, #>Bitmap
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;;Let draw some stuff
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LDX #$00
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LDA $FE
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ORA ($49, X)
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STA ($49, X)
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RTS
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.endproc
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