provided unofficial $E50C routine - for compatibility

c64/kernal/e50a.plot.s

@@ -0,0 +1,29 @@
+
+//
+// Official Kernal routine, described in:
+//
+// - [RG64] C64 Programmer's Reference Guide   - page 290
+// - [CM64] Compute's Mapping the Commodore 64 - page 215
+//
+// CPU registers that has to be preserved (see [RG64]): none
+//
+
+PLOT:
+	bcs plot_get
+
+	// Note: the 'set' part has to start from $E50C, as this is a known address
+	// - https://www.lemon64.com/forum/viewtopic.php?t=3296&amp%3Bstart=15
+	// - 'Duotris' game calls $E50C during startup screen initialization
+
+plot_set:
+	sty TBLX
+	stx PNTR
+
+	// XXX handle cursor blink
+
+	// FALLTROUGH to save one byte on RTS
+
+plot_get:
+	ldy TBLX
+	ldx PNTR
+	rts