SCREEN START 0 
    LDA #65
    JSUB scrfill
    JSUB scrclear    

HALT J HALT
    END SCREEN

scrfill     STA znak    
loop        LDA y 
            MUL scrcols
            ADD screen
            ADD x
            STA pix_ptr
            LDA znak
            STCH @pix_ptr
            LDA x
            ADD #1
            STA x
            COMP scrrows
            JLT loop
            CLEAR A
            STA x
            LDA y
            ADD #1
            STA y 
            COMP scrcols
            JLT loop
            
            LDA znak
            RSUB


.address = screen + y * scrcols + x
scrclear    LDA y 
            MUL scrcols
            ADD screen
            ADD x
            STA pix_ptr
            CLEAR A
            STCH @pix_ptr
            LDA x
            ADD #1
            STA x
            COMP scrrows
            JLT scrclear
            CLEAR A
            STA x
            LDA y
            ADD #1
            STA y 
            COMP scrcols
            JLT scrclear
        
            CLEAR A
            STA x
            STA y
            RSUB        
  


znak WORD 0 
x WORD 0 
y WORD 0
pix_ptr WORD 0 
screen WORD X'00B800'
scrcols WORD 25 
scrrows WORD 80
scrlen WORD 2000