Lab 2

Lab 2 was are introduction to the 6052 Emulator and write coding  about creating lines on the emulator.


In the introduction to the emulator we learned that the tya command switch the value in y to a leaving you with 16 vertical stripes. The lsr command leads to the amount of pixels doubling for example 1 lsr gives you pixels in groups of two 2 lsr gives you pixels in groups of 4 and so on. This happens because the lsr command is shifting all the binary bits one to the right then adding a zero at the front. Next we have the asl command that get rides of have the colors each time because the leftmost bit is erased and a zero added at the right end. Lastly the iny command files in the screen skipping how many pixels the increase is by until the loop reaches its end.

Code Green and Blue lines

This code draws a green line at the very top and a blue line at the very bottom

    lda #$00    ; set a pointer at $40 to point to $0200 -top left of screen 

    sta $40 

    lda #$02 

    sta $41

    lda #$e0    ; set a pointer at $40 to point to $0200 -bottom left of screen 

    sta $42 

    lda #$05 

    sta $43

    ldy #$00    ; set index to 0 

  

loop:    lda #$05    ; colour = green 

    sta ($40),y    ; set pixel

    lda #$06    ; colour = blue 

    sta ($42),y    ; set pixel

    iny        ; increment index 

    cpy #$20    ; 

    bne loop    ; continue until done the page

 

Code Purple and Yellow lines

This code draws a green line at the very top, a blue line at the very bottom, a yellow line on the left side and a purple line on the right.

    lda #$00    ; set a pointer at $40 to point to $0200 - top left of screen 

    sta $40 

    lda #$02 

    sta $41

    lda #$e0    ; set a pointer at $42 to point to $05e0 - bottom left of screen 

    sta $42 

    lda #$05 

    sta $43

    ldy #$00    ; set index to 0 

  

loop:    lda #$05    ; colour = GREEN 

    sta ($40),y    ; set pixel

    lda #$06    ; colour = BLUE 

    sta ($42),y    ; set pixel

    iny        ; increment index 

    cpy #$20 

    bne loop    ; continue until done the page     

  

loop2:    ldy #$0        ; left side 

    lda #$07    ; colour = YELLOW 

    sta ($40),y    ; set pixel

    ldy #$1F    ; right side 

    lda #$04    ; colour = PURPLE 

    sta ($40),y    ; set pixel 

  

    clc        ; clear the carry before doing any additions 

    lda $40        ; get the low byte of the pointer 

    adc #$20    ; add 20 hex to move down one line 

    sta $40        ; save the new pointer 

    bcc loop2    ; if the carry bit is clear then we are still inside a page 

  

    inc $41        ; otherwise update the page pointer 

    lda $41        ; get the current page address 

    cmp #6        ; have we reached beyond the last page 

    bne loop2    ; nope