; TV-noise for the ZX81
    ; by Andreas 'Shadow/Noice' Gustafsson
    ; 2010-11-13
       
       ld    hl,(400ch)       
       ld    de,24*33         
       add   hl,de           
       ld    de,7618h    ; d=halt opcode, e=y loop counter
       ld    (hl),d      ; Ending halt
    yloop:                   
       ld    b,32   
    xloop:         
       dec   hl     
       and   63          ; Make sure we have a legal char
       ld    (hl),a       
       inc   a
       djnz  xloop
       add   a,e         ; Add y to char to get more 'randomness'
       dec   hl               
       ld    (hl),d     
       dec   e                 
       jr    nz,yloop
    infloop:   
       and   15          ; Stick with lowest 4k of ROM so we don't get the real charset, just random data
       inc   a
       ld    i,a 
       jp    infloop