SCREEN-DELETION-WITH-RANDOM-VALUES
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TOOL: 		EDASS-128 Editor/Assembler {Commodore C128}
Language: 	Assembler
Extra:		-
Author: 	Misel Zivanovic
Note:		(C) 26th April 2026  - www.lived.ch, mzretro.ch

Information:	I had to update this doc, 29.04.2026. The first address i used caused the issues
		with the SFK {Set Function Keys}. I forgot that it uses the space from $0b00 and
		this random deletion code went slightly over $0b00.
		Ergo, SFK didn't work correctly anymore! 
		You can assembly this routine despite all that from $0ac8 because later you won't
		need SFK anyway. 
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This little code will delete your screen. And it will do that by making little squares disappear 
from your screen. To make the effects complete and also to make sure the full content will be 
delete, a *ROM-Routine is used at the end to delete the screen completely

*Note:
C128 ROM-Routines can be called only if you are using BANK 15!
Also generating and getting the random numbers will work only there!
That being said, you could have your code also in BANK 0 and then just switch to BANK 15, call the
ROM-Routine{s} and switch back to BANK 0 again. *** We don't do that here ***! Only BANK 15 is used!

To test the assembler code, run this BASIC LINE below in BASIC 7.0 {DIRECT MODE, NO LINE NUMBERS!!!}
Just copy and paste it after the assembler code is available in the memory 
{meaning it must be assembled after you have all typed in or did a copy/paste within the EDASS-128}



{C128 BASIC 7, test code! Assembly part below must be in the memory before you start this!}

fora=1024to2023:pokea,224:next:char1,0,4,"sys 4864 :::"+chr$(19):poke842,13:poke208,1:end


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Project-Name and source code: Can be called with SYS 2760 from BASIC
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HINT FOR C64 USERS: To make this code also 100% Commodore C64 compatible:

1st - REMOVE sta $ff00
2nd - REPLACE jsr $c142     ; clear screen
      with    jsr $e544     ; clear screen
      OR with 
              lda #$93
              jsr $ffd2

3rd - USE C64 suitable memory are, e.g. $0340 or higher e.g. $c000 depending on the assembler editor
      you are going to use on the C64 side. {there is EDASS-64 existing for the Commodore C64 too!}
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; screen deletion as a random pattern
; looks good and needs a little space
; placed low from $1300 to not disturb
;
; note: you can also use even lower 
; addresses, e.g. from $ac8 and up
; until $0dff (sprites are from $0e00)
; but then SFK won't work because it
; is in that region!
; not important when you don't use
; EDASS-128
; 
;26.04.2026
;
         *=  $1300
         .obj m
         .bank 15
;
         lda #$00
         sta value
         sta $ff00     ; bank 15
;-------------------------------
         lda #$ff      ; random numbers
         sta $d40e     ; check compute
         sta $d40f     ; mapping c128
         lda #$80      ; for more info.
         sta $d412
;-------------------------------
 loop1   ldy #$00
 loop2   lda $d41b     ; read random #
         tax
         lda #$20      ; space to delete
         sta $0400,x   ; screen 1st part
         sta $0600,x   ; screen 3rd part
         lda $d41b     ; get new rnd #
         tax
         lda #$20
         sta $0500,x   ; screen 2nd part
         sta $06e8,x   ; screen 4th part
         iny
         cpy #$08      ; repeat 8x
         bne loop2
         lda #$e0      ; wait on the
 a1      cmp $d012     ; raster line
         bne a1        ; to slow things
         lda value
         tay
         iny
         tya
         sta value
         cpy #$85      ; repeat all
         bne loop1     ; $85, dec 133
;                        times
         jsr $c142     ; clear screen
         rts           ; back to basic
 value   .byte 0