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libsrc/cbm610/crtc.s

@@ -0,0 +1,58 @@
+;
+; Ullrich von Bassewitz, 28.09.1998
+;
+; Write to the CRTC.
+;
+
+ 	.export	       	write_crtc, read_crtc
+	.importzp	crtc
+
+	.include      	"cbm610.inc"
+	.include      	"zeropage.inc"
+
+
+; Write a value to the CRTC. The index is in Y, the value in A
+
+.proc	write_crtc
+	sta	sedt1
+	lda	IndReg
+	pha
+	lda	#$0F
+	sta	IndReg
+	tya
+	ldy	#$00
+	sei
+	sta	(crtc),y
+	iny
+	lda	sedt1
+	sta	(crtc),y
+	cli
+	pla
+	sta	IndReg
+	lda	sedt1
+	rts
+.endproc
+
+
+.proc	read_crtc
+	sty    	sedt1
+	lda	IndReg
+	pha
+	lda	#$0F
+	sta	IndReg
+	lda    	sedt1
+	ldy	#$00
+	sei
+	sta	(crtc),y
+	iny
+       	lda	(crtc),y
+	cli
+	tay
+	pla
+	sta	IndReg
+	tya
+	ldy    	sedt1
+	rts
+.endproc
+
+