diff --git a/vt100.screen.S b/vt100.screen.S
index ebf309c..4a3677a 100644
--- a/vt100.screen.S
+++ b/vt100.screen.S
@@ -93,11 +93,18 @@ enable_cursor ent
 cursor_vector	ent
 	jml cursor_int
 
+NumInts	equ $e01d67
+
 cursor_int
 * cursor interrupt - blink the cursor.
 
 	mx %11
 
+* check if CDA active.
+* $ff = inactive, $00 = active
+	lda >NumInts
+	bpl :rts
+
 	ldy cursor_offset
 
 	lda cursor_state