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libsrc/pet/clrscr.s

@@ -0,0 +1,50 @@
+;
+; Ullrich von Bassewitz, 26.11.1998
+;
+; void clrscr (void);
+;
+
+	.export	    	_clrscr
+	.import		plot
+       	.importzp   	ptr1
+	.import	    	xsize
+
+	.include    	"pet.inc"
+
+_clrscr:
+
+; Set the screen base address
+
+	lda	#$00
+	sta	ptr1
+	lda	#$80
+	sta	ptr1+1
+
+; Determine, how many pages to fill
+
+	ldx 	#4
+	lda	xsize
+	cmp	#40
+       	beq	L1
+	ldx	#8
+
+; Clear the screen
+
+L1:    	lda    	#$20		; Screen code for blank
+	ldy	#$00
+L2:	sta	(ptr1),y
+   	iny
+   	bne	L2
+   	inc	ptr1+1
+	dex
+	bne	L2
+
+; Set the cursor to 0/0
+
+	lda	#0
+	sta	CURS_X
+	sta	CURS_Y
+	jmp	plot
+
+	rts
+