diff --git a/src/mess/machine/vcsctrl.h b/src/mess/machine/vcsctrl.h
index a35f63e82eb..ff9837d45aa 100644
--- a/src/mess/machine/vcsctrl.h
+++ b/src/mess/machine/vcsctrl.h
@@ -46,6 +46,18 @@ public:
 	virtual ~vcs_control_port_device();
 
 	// computer interface
+
+	// Data returned by the joy_r methods: 
+	// bit 0 - pin 1 - Up
+	// bit 1 - pin 2 - Down
+	// bit 2 - pin 3 - Left
+	// bit 3 - pin 4 - Right
+	// bit 4 - pin 5 - 
+	// bit 5 - pin 6 - Button
+	//         pin 7 - +5V
+	//         pin 8 - GND
+	// bit 6 - pin 9 - 
+	//
 	UINT8 joy_r();
 	DECLARE_READ8_MEMBER( joy_r );
 	UINT8 pot_x_r();