implemented PLOT routine

STATUS.md

@@ -108,7 +108,7 @@ NOTE: Even the 'DONE' routines won't support features described as missing in on
 | `$FFE7`   | `CLALL`  | DONE     |                                                    |
 | `$FFEA`   | `UDTIM`  | DONE     |                                                    |
 | `$FFED`   | `SCREEN` | DONE     |                                                    |
-| `$FFF0`   | `PLOT`   | NOT DONE |                                                    |
+| `$FFF0`   | `PLOT`   | DONE     |                                                    |
 | `$FFF3`   | `IOBASE` | DONE     |                                                    |
 
 <br />

c64/kernal/plot.s

@@ -9,4 +9,19 @@
 ;;
 
 plot:
+	bcs plot_get
+
+plot_set:
+	sty current_screen_y
+	stx current_screen_x
+
+	;; Our implementation has different screen editor, updating any
+	;; other variables (see [CM64]) seems to be unnecessary
+
+	;; FALLTROUGH to save one byte on RTS
+
+plot_get:
+	ldy current_screen_y
+	ldx current_screen_x
 	rts
+