Stereoscopic/monoscopic video display system

A stereoscopic video display device includes a left and a right video display for viewing by respectively the left and right eye of a viewer, a video driver circuit which alternates between driving the left video display and driving the right video display, and a view control circuit for providing a left-right signal which indicates which video display is currently displaying the video signal. A video signal source, such as a computer or a video game console, receives the left-right signal and provides a standard video signal. The stereoscopic display is usable with a source that provides a video signal that represents a left or right view according to the left-right signal, or with a source that ignores the left-right signal and provides a monoscopic video signal. The stereoscopic display is operable in both a stereo and a mono mode so that a user can select either monoscopic or stereoscopic video when the source is capable of providing stereoscopic views.

CROSS-REFERENCES TO RELATED APPLICATION 
This application is related to, and incorporates by reference, commonly 
owned U.S. patent application Ser. No. 08/177,815 entitled "Communication 
Protocol," attorney docket No. M-2574, filed on the same date as the 
present application. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to apparatuses and methods for selectably providing 
either monoscopic or stereoscopic video display in a system which may 
include a variety of video display devices. 
2. Description of Related Art 
Depth perception is well known to be primarily a result of the left and 
right eyes seeing objects from different view points. The brain combines a 
left eye view and a right eye view, through an instinctive use of 
triangulation, to perceive three dimensions. Most common video displays, 
such as televisions, are unable to provide images that appear three 
dimensional because the displays provide only a single view and 
triangulation which penetrates the view is not possible. Stereoscopic 
video displays attempt to provide a different view to each eye. If the two 
different views are sufficiently close to left and right eye views of an 
actual object, the brain combines the two views and perceives a three 
dimensional image. 
One stereoscopic display method uses a single display and special 
spectacles which change an image on the display differently for each eye. 
Common examples include spectacles with different color filters, different 
polarization filters, or shutters which alternately blank left and right 
eyes. Generally, the associated single screen images are blurry when 
viewed without the special spectacles. 
Other stereoscopic display methods employ separate left and right displays, 
for viewing by left and right eyes of a viewer. Such methods typically 
require special video signals and special image processing circuits, and 
cannot be used with monoscopic displays. 
Most existing systems and video games are monoscopic only and not designed 
to operate with stereoscopic displays. This lack of stereoscopic images 
limits the attractiveness of such prior art games, especially for "virtual 
reality" applications. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, the capabilities of video game 
systems can be expanded to optionally include stereoscopic images and 
displays. Such systems can be implemented on existing game consoles that 
were not designed for producing stereoscopic images, and are compatible 
with existing monoscopic displays such as televisions and video monitors 
so that games that work with stereoscopic displays also work on 
conventional televisions. Further, for people who have difficulty viewing 
stereoscopic video or people who prefer monoscopic video, the stereoscopic 
displays are operable in monoscopic mode. 
In accordance with the present invention, a stereoscopic video display 
device includes a left and a right video display for viewing by 
respectively the left and the right eye of a viewer, a driver circuit 
which alternates between driving the left and the right video display, and 
a view control circuit for providing a left-right signal which indicates 
which video display is currently displaying the video signal. Typically, 
the left and right video displays are small (e.g. LCD) displays mounted on 
a helmet and having an associated optical system for viewing the left 
display with the left eye and the right display with the right eye. 
Video displays in accordance with the invention may be used with a video 
signal source, typically a computer or a video game console, which 
receives the left-right signal from the display and provides a video 
signal representing left or right view depending on the left-right signal 
value. Many known sources of video signals which have at least one 
available input lead can be programmed to generate stereoscopic video and 
be used with the stereoscopic video displays, even if the source is not 
specifically designed for stereoscopic video. The stereoscopic display is 
also usable with a source that ignores the left-right signal and provides 
a video signal that represents a monoscopic view. 
In one embodiment, the driver circuit in the stereoscopic display is 
operable in both a stereo mode and a mono mode. In stereo mode, the driver 
circuit alternately drives the left video display and then the right video 
display, and the left-right signal requests a left or right view according 
to the active display. In mono mode, the video signal is simultaneously 
routed to both the left and right displays so that left and right eyes of 
a viewer see the same images, and the left-right signal always requests 
the same view. 
Another embodiment in accordance with the invention is a stereoscopic video 
system that includes a display as described above along with a source of 
video signals capable of interpreting the left-right signal and acting 
accordingly. 
In still another embodiment, an interface box is provided as part of the 
stereoscopic display and provides a convenient location for circuitry. 
With the interface box, the head mounted portion of the display can be 
made lighter and retrofitting of circuitry in the video signal source is 
avoided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1A shows an embodiment of a stereoscopic video display system in 
accordance with the present invention. The system includes a video signal 
source 110, an interface box 120, and a head mounted display 130. Video 
signal source 110 may for example be a conventional computer or video game 
console executing a program (video game). In one embodiment, video signal 
source 110 (only relevant portions of which are shown in FIG. 1A) is a 
commercially available SEGA GENSIS.TM. video console executing a program 
provided by a game cartridge or a CD ROM drive unit. 
Digital systems such as computers or game consoles typically employ VRAM 
(video random access memory) to store a digital representation of a video 
image. VRAMs 116 and 118 are frame buffers which store digital 
representations of respectively a left view and a right view generated 
according to the program being executed by video signal source 110. VRAM 
116 and 118 each store a single digitized video frame. In other 
embodiments, each VRAM may hold more or less data than a video frame. 
Two VRAMs 116 and 118 provide a convenient way to segregate and store left 
and right views for stereoscopic images. A virtual reality program can 
draw left and right views directly into the respective left and right VRAM 
116 and 118. The views are stored in VRAM 116 and 118 for future revision, 
and one view can be changed while the other view is being displayed. 
However, video signal sources in accordance with the invention are not 
restricted to two VRAMs. A single VRAM can be used for stereoscopic images 
if the video signal source can change or exchange the data in the single 
VRAM fast enough to provide a left view or a right view when needed by a 
video adapter 112. A single VRAM can also be used to supply monoscopic 
video where no swapping of views is necessary. With more than two VRAMs, 
the video signal source can create multiple frames before the frames are 
needed for display purposes. 
Video adapter 112 converts digital images in VRAM 116 and 118 into a video 
signal which is provided on output line 102. The video signal may be 
provided in any desired format. The most common formats are conventional 
analog video signals carried on a single line, for example, an NTSC, , 
RGB, or HDTV signal. The video signals conventionally contain a series of 
video signal frames, each frame representing a still image. The frames are 
supplied and displayed at a fixed refresh rate, such as 50 Hz or 60 Hz. 
The changing data held in VRAM 116 and 118 changes successive frames and 
can simulate a smoothly moving image. Adapters such as adapter 112 which 
generate an analog video signal from digital image data, are well known in 
the art, and commonly used in computers and video game consoles. 
Interface box 120 and head mounted display 130 together constitute a 
stereoscopic display. The video signals from adapter 112 pass through 
interface box 120 to head mounted display 130. In the embodiment of FIG. 
1A, interface box 120 is merely a junction box for lines and cables from 
video signal source 110 and head mounted display 130. In other 
embodiments, interface box 120 is eliminated so that lines directly 
connect video signal source 110 and head mounted display 130. In still 
other embodiments, circuitry such as view control circuit 132 and display 
driver 134 are located in interface box 120 instead of in head mounted 
display 130 as shown in FIG. 1A. FIG. 1B shows a block diagram of an 
alternate embodiment which includes a processor circuit 122 that controls 
communications between head mounted display 130 and video source 110. 
Placing circuitry in interface box 120 instead of in head mounted display 
130 lightens head mounted display 130 but increases the amount of signal 
routing. 
Video signal source 110 may be a computer or a game console not 
specifically designed for use with a stereoscopic display. Adding 
specialized stereoscopic display circuitry to video source 110 may be 
difficult, particularly when source 110 is a game console which has no 
provision for add-on devices in the game console cabinet. Accordingly, 
placing any additional circuitry in the stereoscopic display makes adding 
stereoscopic capabilities to a game console easier, and reduces the cost 
of a game console without stereoscopic capabilities. 
Head mounted display 130 contains a left video display 136 and a right 
video display 138. Video displays 136 and 138 may each be, for example, a 
liquid crystal display (LCD), a small cathode ray tube (CRT), or a 
projection system. Driver circuit 134 drives video displays 136 and 138 by 
converting the video signal from video signal source 110 to the proper 
format for video displays 136 and 138 and providing the converted signals 
to selected displays 136 and/or 138. 
Video displays 136 and 138 are mounted on a helmet or other head gear (not 
shown) and positioned so that the left eye of a viewer wearing the helmet 
sees left video display 136, and the right eye of the viewer sees right 
video display 138. Many different optical systems, for example, a 
magnifier eyepiece lens system directly between each of displays 136 and 
138 and the viewer's eyes or a focusing mirror system which permits 
viewing of a reflected image, may be employed for viewing video displays 
136 and 138. U.S. patent application Ser. No. 07/832,237, by Richard 
Dennis Rallison, entitled "Optically Corrected Helmet Mounted Display" is 
incorporated by reference herein in its entirety and discloses a heads up 
display that can project an image from video displays 136 and 138 to the 
eyes of the viewer and can combine the projection with a direct view of 
the surrounding environment. 
The stereoscopic display is operable in two modes, a stereo mode and a mono 
mode. In stereo mode, left and right displays 136 and 138 are configured 
to display a stereoscopic image. In mono mode, left and right displays 136 
and 138 are configured to display a monoscopic image. The operating mode 
may be set for example by a switch provided either on head mounted display 
130 or on interface box 120. The mode may also be set by command signals 
from video signal source 110. A protocol for sending such command signals 
to head mounted display is disclosed in the U.S. patent application 
entitled "Communication Protocol", incorporated by reference above. 
In the embodiment shown in FIG. 1A, driver circuit 134 routes video signal 
to left video display 136 and/or right video display 138, and controls 
which display 136 or 138 displays the image represented by the signal. For 
example, in stereo mode, a video frame is shown on left video display 136, 
then the following frame of video frame is shown on right video display 
138, then a frame on left display 136, and so on alternately showing 
frames on the left then right displays. In one embodiment, driver circuit 
134 controls the displays by alternately routing video information to the 
left display 136 then the right display 138. In another embodiment, driver 
circuit 134 routes video information to both displays 136 and 138 
simultaneously and enables one display 136 or 138 while disabling the 
other display 138 or 136 so that left and right views are only shown on 
the correct display. In still another embodiment, driver circuit 134 route 
video signals to both displays and view control circuit 132 provides the 
signals which enables or disables display 136 or 138. 
In the embodiment of FIG. 1A, view control circuit 132 sends a left-right 
signal to source 110 along line 104. The left-right signal may for example 
be a digital signal having a value of high or low, which indicates a 
desired view. In the stereo mode, view control circuit 132 can either 
control driver circuit 134 so that driver circuit 134 operates video 
displays 136 and 138 in agreement with the left-right signal, or can 
monitor driver circuit 134 and provide a left-right signal in agreement 
with the activated display 136 or 138. 
In the embodiment of FIG. 1B, processor circuit 122 in interface box 120 
controls communication between head mounted display 130 and video source 
110. A single line 106 is sufficient to convey the left-right status 
signal to interface box 120. Processor circuit 122 communicates with video 
source 110 through a bus 104 and an I/O port. In an embodiment where video 
source 110 is a game console such as a SEGA GENESIS.TM. video game 
console, an I/O port which is commonly used for a joystick provides as 
interface for communicating the left-right status and communicating data 
to and from processor circuit 122. Such communications can include 
transmission of the left-right signal from view control circuit 132, data 
from a headtracker circuit 135, or a stereo-mono control signal for 
controlling whether view control circuit 132 is in stereoscopic or 
monoscopic mode. Video source 110 provides either the left or the right 
view according to the left-right signal so that in stereo mode, the views 
are synchronized, left or right, with the active display, left display 136 
or right display 138. 
In video signal source 110, a game program controls the video image 
according to the state of the left-right signal. Typically, a memory 
location in video signal source 110 is dedicated to holding the base 
address of a memory block which holds the image data used by adapter 112. 
Adapter 112 retrieves the base address from the dedicated memory location 
before generating each video frame. The game program changes from left 
view to right view by writing an appropriate address into the dedicated 
memory location. The game program can also change the image by changing 
data in the VRAM 116 or 118 used by adapter 112. In an alternative 
embodiment, a multiplexer selectably connects VRAM 116 or 118 to adapter 
112. In still another alternative embodiment, more than one adapter, each 
addressing a different location in VRAM 116 or 118, may have output video 
signals routed by a multiplexer which selects the video signal that is 
sent to the stereoscopic display. 
The value of the left-right signal depends on the operating mode of display 
driver circuit 134 and view control circuit 132 and on which of the 
displays 136 or 138 is active. In stereo mode, view control circuit 132 
provides a left-right signal which when left display 136 is active, 
requests that video signal source 110 provides a left view, and when right 
display 138 is active, requests that video signal source 110 provides a 
right view. 
In mono mode, both displays 136 and 138 are activated, and view control 
circuit 132 provides a left-right signal that always requests the same 
view. Accordingly, left display 136 and right display 138 display the same 
frames, and both eyes of a viewer see the same view (monoscopic video.) 
Thus in the mono mode, a monoscopic video display such as a television 
coupled to video signal output line 102 displays a clear image, and both 
the head mounted display and the monoscopic video display may be 
simultaneously connected to video signal source 110. In stereo mode, a 
monoscopic display such as a television coupled to line 102 would 
undesirably flash left and right images and provide a jumpy image that is 
difficult to view. 
In one particular embodiment, adapter 112 provides a standard NTSC or 
video signal, and driver circuit 132 causes one video display 136 or 138 
to display a full frame before causing the other of video display 136 or 
138 to display a frame. The change from one video display to the other 
occurs during the video vertical blanking interval. Driver circuit 134 
monitors the video signal to determine when vertical blanking occurs. View 
control circuit 132 receives from driver circuit 134 a signal indicating 
the vertical blanking interval and then sends the left-right signal 
requesting the correct view for the next frame. 
In another embodiment, video signal source 110 sends a request for 
information to the stereoscopic display during the vertical blanking 
interval, and view control circuit 132 responds by providing data 
including the left-right signal. 
In stereoscopic mode, while driver circuit 134 activates one of the video 
displays 136 or 138, the other of video displays 136 or 138 is not 
displaying a new frame so that one video display 136 or 138 shows even 
frames from the video signal and the other video display 138 or 136 shows 
odd frames from the video signal. The frame rate (or refresh rate) of 
displays 136 and 138 is therefore half the standard rate, for NTSC, thirty 
frames per second instead of sixty frames per second. For most animation, 
thirty frames a second is sufficient to simulate smooth motion. LCDs, 
which retain images longer than do CRTs, reduce flickering caused by 
fading of an image between refreshes. 
FIG. 2 shows video signal source 110 coupled to a monoscopic video display 
230. Monoscopic video display 230 may be a television, a monitor, or any 
display compatible with the video signal on line 102. Lead 104, which is 
for accepting a left-right signal, is not connected. Accordingly, no 
left-right signal is provided to switch the video signal between a left 
and a right view. Video signal source 110 may have a pull-up or pull-down 
circuit that ensures the voltage on line 104 is constant when no external 
signal is applied to line 104. The video signal from adapter 112 provides 
the same view, for example always the left view, because the left-right 
signal is constant. The resulting video signal provided to monoscopic 
display 230 represents a constant view (either left or right) and is at 
the standard frame rate of the video signal source 110. Accordingly, video 
source 110 may be used with monoscopic displays. 
FIG. 3 shows a block diagram of stereoscopic head mounted display 130 and 
interface box 120, coupled to monoscopic video signal source 310. Video 
signal source 310 differs from video signal source 110 of FIG. 1, in that 
video signal source 310 does not generate a left and a right view. Video 
signal source 310 may be for example a video game console identical to the 
video game consoles disclosed in FIG. 1, except the video game console in 
FIG. 3 is executing a program which does not implement stereoscopic video. 
A program which is not designed for stereoscopic video but which uses 
signals on line 104, may misinterpret left-right signals. If the program 
is incorrectly interpreting the left-right signal on line 104, the user 
can disconnect line 104 from interface box 120. Alternatively, 
stereoscopic display 130 can use a communications protocol which prevents 
sending of a left-right signal if source 110 does not respond properly. 
Video signal source 310 provides a conventional video signal that does not 
switch between left and right views, therefore left and right displays 136 
and 138 show the same view. Even if head mounted display 130 is in stereo 
mode and routes the video signal alternately to left display 136 then 
right display 138, both displays 136 and 138 show the same view (separated 
in time by one frame). Accordingly, the system automatically adjusts to 
provide a monoscopic video display if video signal source 310 only 
provides monoscopic video. 
FIG. 4 shows a block diagram of an embodiment of interface box 120 and head 
mounted display 130 which are used in a system that includes a SEGA 
GENESIS.TM. video game console (not shown) as the video signal source. 
SEGA GENESIS.TM. video game consoles are widely available commercially and 
not described in detail here. The SEGA GENESIS.TM. video game console 
supplies a video signal, a left audio signal, and a right audio signal 
through RCA jacks J1, J2, and J3 respectively to a printed circuit board 
(PCB) 420. Audio signals may also be provided to PCB 420 from a device 
such as a CD ROM drive through a stereo mini jack J8. Two-way 
communications with the Genesis, described in more detail below, are 
conducted through port J6. Port J7 receives a constant 13.5 volt DC power 
supply. 
PCB 420 is a communications interface and provides video and audio signals 
to peripheral devices such as head mounted display 130. Analog video and 
audio signals are provided from PCB 420 through port P1 to port J1A of a 
PCB 430 mounted on head mounted display 130. Two way digital communication 
is provided on bus 425 between PCBs 420 and 430 via ports P2 and J1B. PCB 
430 contains a view control circuit and a display driver, and controls 
left and right video displays 136 and 138 (and back lights 436 and 438 for 
the displays) via ports J9, J10, and J11. 
FIGS. 5-7 show circuit diagrams of the elements on PCB 420 of FIG. 4. The 
circuit in FIG. 5 routes the video signal from jack J1 onto line 
VIDEO.sub.-- TO.sub.-- IF for transmission to head mounted display 130. 
Circuitry 510 provides a signal on line NO.sub.-- VIDEO.sub.-- TO.sub.-- 
IF indicating whether a video signal is being received on jack J1. 
Circuitry 520 similarly provides a signal indicating if an audio signal is 
being received from the video game console on either jack J2 or J3. 
FIG. 6 shows circuitry 610 which provides the audio signals either from 
jacks J2 and J3 or stereo mini jack J8 to port P1 and audio jacks J4 and 
J5. The audio signals may be provided through lines AUDIO.sub.-- R.sub.-- 
HMD and AUDIO.sub.-- L.sub.-- HMD to headphones (not shown) in the head 
mounted display 130 or to an external amplifier (not shown) through jacks 
J4 and J5. Also shown in FIG. 6 are the lines which connect to port P1 and 
supply signals for head mounted display 130. Lines VIDEO.sub.-- TO.sub.-- 
IF, AUDIO.sub.-- L.sub.-- HMD, and AUDIO.sub.-- L.sub.-- HMD carry analog 
video and audio signals. Lines NO.sub.-- VIDEO.sub.-- TO.sub.-- IF and 
NO.sub.-- AUDIO.sub.-- TO.sub.-- IF carry digital signals indicating 
whether interface box 120 is receiving video or audio signals. The 
remaining lines connected to port P1 carry fixed reference or power supply 
voltages. 
In FIG. 7, circuitry 710 provides power supply voltages. FIG. 7 also shows 
interface circuitry which controls communications. Connector J6 connects 
to the second joystick port of the video game console via a standard 
cable. Static filter 720 filters out noise in the cable connected to the 
video game console. In one embodiment, static filter 720 is a part No. 
4420R-601-470/500 available from Bourns, Inc. 
When connector J6 is connected to the joystick port, the video game console 
pulls lines SON and ON high. When connector J6 is not connected to a 
joystick port, a pull-down resistor 742 pulls the voltage on line ON low. 
A microprocessor 730 senses a low signal on line ON when connector J6 is 
not connected, and resets the head mounted display and sensors to a 
default mode. In one embodiment, microprocessor 730 is an MC68HC711E9 
available from Motorola. Reset switch 750 and debouncing circuit 745 
connect line ON to ground and also reset the displays and sensors into the 
default mode. Pull-up resistors 740 fix the voltages on lines UP, DOWN, 
LEFT, RIGHT TL, TH, and TR when no external signals are applied to 
connector J6. 
Connector P2 and static filter 780 are for connecting to head mounted 
display 130 which includes PCB 430 in FIG. 4, video circuitry 136, 138, 
436, and 438, and head tracker 440. Head tracker 440 senses and provides 
angles indicating the orientation of head mounted display 130. Suitable 
head trackers are well known in the art and include sensors such as bubble 
levels and flux compasses which determine angles relative to the direction 
of gravity or the earth's magnetic field. 
Memory in microprocessor 730 holds a program which implements a 
communications protocol used for communications between the video game 
console and head mounted display 130 (and/or other peripheral devices). 
The protocol includes formats for sending a left-right signal to the video 
game console, sending data to the Genesis, and sending configuration data 
to the head mounted display 130. 
Information is asynchronously transferred between the video game console 
and interface box 120 according to the protocol. Communication protocol 
lines TR, TH, and TL carry handshaking signals, and lines UP, DOWN, LEFT, 
and RIGHT carry parallel signals representing a nibble of information. 
During a periodic data transfer from display 130 to the Genesis, one 
nibble sent to the Genesis contains a bit which is the left-right signal 
that requests either a left or right view from the Genesis. Other nibbles 
in the data packet contain information such as orientation angles measured 
by head tracker 440. During transfer of command packets from the Genesis 
to interface box 120, some nibbles contain bits which indicate how to 
configure head mounted display 130, for example one bit indicates either 
stereo mode or mono mode operations. Further detail of the communications 
protocol is provided in the U.S. patent application entitled 
"Communication Protocol" incorporated by reference above. Microprocessor 
730 also provides the signals necessary for communication with head 
mounted display 130 and other peripherals connected to port P2. 
Pull-up resistors 731 and switches 732 and 733 configure microprocessor 730 
for testing. 
FIGS. 8-14 show circuits contained in head mounted display 130. 
FIGS. 8, 9, and 10 show a circuit diagram of a display driver and a view 
control circuit including chips IC1, IC2, and IC3 which are respectively 
part nos. CXA1585Q, CXA1515Q, and CXD2403R each commercially available 
from Sony. 
As shown in FIG. 8, a video signal is provided from interface box 120 
through the port J1A and a line VIDEO.sub.-- IN. IC1 is an RGB decoder 
which converts the video signal on line VIDEO.sub.-- IN into red, blue, 
and green signals on output lines R.sub.-- OUT, B.sub.-- OUT, and G.sub.-- 
OUT and a synchronization signal on line SYNC. IC2, in FIG. 9, is a RGB 
driver that converts the red, blue, and green signals from lines R.sub.-- 
OUT, B.sub.-- OUT, and G.sub.-- OUT into LCD panel compatible red, blue, 
and green signals on lines D.sub.-- R.sub.-- OUT, D.sub.-- B.sub.-- OUT, 
and D.sub.-- G.sub.-- OUT and a frame start signal on line FRP. Line BF 
carries a burst flag signal. Line VCOM.sub.-- OUT carries a vertical 
control signal. 
IC3, in FIG. 10, is a timing generator which controls operation of IC1 and 
IC2 and a pair of Sony LCX003ZK 0.7-inch NTSC Color LCD panels which are 
connected to ports J9 and J10. Lines VST1 and VST2 carry signals from IC3 
that control when a frame begins on the left or right LCD panel 
respectively. In mono mode, a signal on line 3D is high, and signals on 
VST1 and VST2 simultaneously activate both LCD panels so that both 
displays receive and display the video information. In stereo mode, 
signals on lines VST1 and VST2 alternately activate the left and then the 
right LCD panel in accordance with the left-right signal on line 3DRL so 
that LCD panels 136 and 138 alternate showing frames. 
FIG. 11 shows a circuit 1110 for powering back lights 436 and 438 of LCD 
panels 136 and 138, a view control circuit 1120 for generating the 
left-right signal, and a circuit 1130 for selecting either mono mode or 
stereo mode video. In view control circuit 1120, a NOR gate 1121 provides 
a signal that triggers a D flip-flop 1122 every time either LCD begins a 
frame (every frame). Flip-flop 1122 has an inverted output lead Q 
connected to input lead D so that an output signal on lead Q changes every 
frame. The output signal from lead Q is provide to an EXOR gate 1124 and 
in normal operation, is inverted by EXOR 1124 to provide the left-right 
signal on line 3DLR. 
Switch 1123 manually resets flip-flop 1122 to start a first frame on the 
left. The video game console, by sending appropriate data to 
microprocessor 730, can set the signal on line COM0 and reset flip-flop 
1122. Switch 1125 changes the left-right signal between normal and reverse 
stereoscopic operation. Normal and reverse operation can also be 
configured by the video game console sending appropriate data to 
microprocessor 730 which, in turn, sets the signal on line COM2. In normal 
stereoscopic operation, the left video frames are sent to left video 
display 136, and the right video frames are sent to right video display 
138. Reverse stereoscopic operation switches the video frames left for 
right, and typically would only be used for testing hardware and debugging 
software. 
Mono mode and stereo mode are set through circuit 1130, manually by 
operating switch 1131 or through software by resetting the signal on line 
COM1. 
FIG. 12 shows a interface circuit in PCB 430 for communications with PCB 
420. Signals are sent to and received from PCB 420 on port J1B. Noise is 
filtered out of the signals by filter 1210. Signals received from PCB 420 
are transmitted either to command lines COM0-COM7 through 
serial-to-parallel converter 1220 or to head tracker 440 through port J12. 
Signals sent to PCB 420 come either from lines ERROR0-ERROR7 via 
parallel-to-serial converter 1230 or head tracker 440. When signals on 
lines FD00 and CONT are low, a signal on line TCK clocks bits from 
parallel-to-serial converter 1230 though logic gates 1240 and onto line 
TDO. 
FIGS. 13 and 14 shows circuitry which generates signals on lines ERROR1 and 
ERROR3-ERROR7. (Signals on lines ERROR0 and ERROR2 indicate whether PCB 
430 is receiving video and audio signals and are provided by interface box 
120 through ports J9 and J1A.) Lines ERROR1 and ERROR3 carry signals that 
indicate whether PCB 430 is receiving video and audio signals on lines 
VIDEO.sub.-- IN, AUDIO.sub.-- R.sub.-- HMD, and AUDIO.sub.-- L.sub.-- HMD. 
Line ERROR4 carries a signal indicating whether PCB 430 is receiving 
power. Line ERROR5 carries a signal indicating whether LCD displays 136 
and 138 are functioning. Line ERROR6 carries the left-right signal from 
line 3DLR which is sent to interface box 120 then to the video game 
console. Line ERROR7 carries a signal indicating whether the head tracker 
is functioning. 
Although the present invention has been described with reference to 
particular embodiments, the description is only an example of the 
invention's application and should not be taken as a limitation.