Video Target PracticeFaye Kasemset Andrew Klock Dave KlosterMIT 6.111 - Introductory Digital Systems LaboratoryProf. Anantha ChandrakasanTA: David MillinerMay13, 2004Table of Contents1.0 Overview Page 12.0 The Nintendo Zapper Interface Page 23.0 Targeting Page 34.0 Video Controller Page 5 4.1 Hardware Description Page 5 4.2 Module Design Descriptions Page 65.0 The Game Controller Page 8 5.1 Sample Timer Page 9 5.2 Random Number Generator Page 9 5.3 Address Selector Page 10 5.4 Control FSM Page 10 5.5 Add FSM Page 11 5.6 Move FSM Page 126.0 Audio Extension Page 137.0 Design and Debugging Issues Page 148.0 Conclusions Page 16Kasemset :: Klock :: Kloster iList of FiguresFigure 1. Overall System Layout and Design Page 1Figure 2. Internal Nintendo Zapper Page 2Figure 3. Internal and Interface Schematic Design Page 2Figure 4. Zapper Signals Page 3Figure 5. Processed Gun Signals Page 3Figure 6. Targeting Mode Controller Inputs and Drawing Page 4Figure 7. Real-Time Targeting Analysis Page 4Figure 8. Video Circuits Page 6Figure 9. Video Module Block Diagram Page 6Figure 10. Major and Minor FSMs Page 7Figure 11. Draw FSMs Write Cycle Timing Diagram Page 8Figure 12. Game Controller Block Diagram Page 9Figure 13. LFSR of Arbitrary Bit Length Page 10Figure 14. Control FSM Transition Diagram Page 11Figure 15. Add FSM Transition Diagram Page 12Figure 16. Move FSM Transition Diagram Page 13Figure 17. Target Movement Page 13Figure 18. Audio Interface Extension Page 14Figure 19. Audio Controller Timing Diagram Page 14Kasemset :: Klock :: Kloster ii1.0 OverviewThe goal of this project is to design and implement a video game system that used a light-gun toread game information from the screen. The overall system layout and design is broken up intothe several parts as seen in Figure 1.Figure 1. Overall System Layout and Design. The Game Controller takes input fromthe system to run the game. The Output Select determines whether the system isdisplaying from the normal Video Output or the Targeting Output. The Zapper andGun Interface read the display information from the RGB monitor controlled by theMC6847 processing circuits.The game is played by using the 1985 Nintendo Zapper to shoot targets on an RGB CRTmonitor. When the player accurately shoots one of three possible targets on the game screen, theKasemset :: Klock :: Kloster 1target that has been hit is removed, and the game score is incremented by one. The targets followand arching pathway across the game screen and progressively get smaller to give the illusionthat they are flying away from the player. There are four levels with forty-four possible targets.2.0 The Nintendo Zapper InterfaceThe interface between the cathode ray tube (CRT) screen and the Nintendo Zapper is thepivoting technology for this project. The Zapper is equipped with a photo-diode and and IRpreamplifier that detects infra-red characteristic beams generated by the electron gun thatescaped from the CRT through the phosphorous screen. Figure 2 shows and internal view of theZapper.Figure 2. Internal Nintendo Zapper. The lens, shielding, and photo-diode are used to filter and detect IR beams from the CRTaccurately up to distances of seven feet.Figure3. Internal and Interface Schematic Diagram. The photo-diode at the top-left ofthe diagram is used by the IR Preamplifier to detect light beams characteristic of a CRT.The transistor and trigger-switch pull down the sensor and trigger signals that must beconnected to 5 volts through 10K resistors in order to work properly. From reversedengineered schematics: Nintendo Entertainment System, Stock # 18-600. ElectronicsCorp. 1992.There are four wires that connect to the Zapper, one each for power, ground, sensor, and trigger.The internal and interface schematic is shown in Figure 3. The biggest secret for interfacing theKasemset :: Klock :: Kloster 2hardware is that the sensor and trigger signals coming from the Zapper are not self-generating.To interface to the Zapper, two 10K pull-up resistors must connect the sensor and trigger signalsto the 5 volt power supply. The Zapper pulls the voltage down using a transistor for the sensorand a push-switch for the trigger.The Gun Interface modules processes the signals coming from the Zapper and puts them in aform more readily usable by the rest of the system. The trigger signal coming from the gun is anactive low signal that stays low for approx. 50 milliseconds when the trigger is pulled once. Thesensor signal is an active high signal that generates 5 millisecond pulses whenever is senses thelight from the CRT. These raw signals can be seen in Figure 4. The Gun Interface modules putsthese signals into active-high signals that are sustained longer and for a constant amount of time.It also adds some filtering to ensure accurate results. The formated signals can be seen in Figure5.Figure 4. Zapper Signals. Lab1-0 is the trigger. Lab1-1 is the sensor. The triggergoes low for anywhere between 50 to 100 milliseconds when pressed once. Thesensor signals generates short pulses when it detects light from the CRT.Figure 5. Processed Gun Signals. The trigger and sensor signals are processed in to shotand hit signals. When the trigger is pressed, the shot signal will go high for 320milliseconds. In state three, the sensor signal is filtered out to allow the time for thescreen to blank before detecting hits. State one listens for the sensor, and when it isdetected, the hit signal goes high and waits in state two until the trigger signal comesdown.The shot signal is sent to the Targeting Mode Controller and to the Output Selector to let themknow when to enter targeting mode. As long as the shot signal is high, the Output Selector givesaddressing control to the Targeting Mode Controller. The hit signal is given to the GameController in conjunction with a target ID from the Targeting Mode Controller module.Kasemset :: Klock :: Kloster 33.0 TargetingTo detect and signal hit targets when
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