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There are two digital-to-analog converters (DACs) on the prototype. One of them is for the Super Nintendo side and one of them is for the CD ROM side. They are muxed together after that. DACs take digital streams and turn them into analog signals – audio in this case. Ben has the prototype hooked up to an Oscilloscope so he can take a closer look at it. He checks the signal for the music from Super Mario Kart and is able to determine that the Super Nintendo DAC is working. The CD rom DAC, which is side by side with the SNES DAC, is not working however.
Ben's been doing some mapping of the schematic and thinks he knows what a mystery chip does. Its probably some sort of BUS location decoder chip. Someone has mapped out what data you send out from the expansion port. The chip let's you talk to other chips on the board based on what type of register is sent out. Ben continues mapping out the chip in order to give him more points from which to test things.
After replacing several questionable capacitors off-camera and jiggling some things around, Ben returns to the shop to find that CD ROM on the Nintendo-Playstation prototype is suddenly working. On the board there is a CD ROM controller chip, a digital signal processor, and there's also a microprocessor on a connected board. When the system is not in game mode, the microcontroller on the connected board tells the CD ROM controller on the motherboard what to do (such as play music). Ben checks the ribbon cables and takes measurements from the three potentiometers on the driver board for the disc.
Ben attempts to get a disc to boot up a game disc. A SNES program is sending commands to the NEC microcontroller, telling it to do disc functions. These commands (and data) would have gone over the expansion bus if this had been a SNES add-on. Super Boss Gaiden loads to black screen so progress has been made. No one has actually made games for the Nintendo-Playstation prototype, the Super Boss Gaiden game was programmed for an emulator. After making adjustments to the burn disc, Ben is able to successfully get a game to run!