JCAP Log #2: JAMMA
Before 1985, most arcade cabinets contained components (printed circuit boards (PCBs), control interfaces, video and sound standards, and power supplies) that were either custom-built or disparate in their implementation. This meant that arcade cabinets were categorically non plug-and-play, so swapping out a different game into a cabinet required a sometimes complete reconfiguration of the internals and therefore a necessarily capable and knowledgeable operator. A need for standardization was recognized, and JAMMA was born.
Original PONG PCB (pre-JAMMA)
JAMMA actually represents a who just as much as it does a what: it's the abbreviation for the Japanese Amusement Machine and Marketing Association. Founded in the early 1980s and headquartered in Tokyo, JAMMA is a trade organization run by representatives of several big-name arcade game manufacturers such as Namco Bandai, Sega, Capcom, Konami, and others.
JAMMA developed a standard for wiring arcade game PCBs to the peripherals of arcade machines, so that anyone could swap out games within the cabinets with others in a way that required a bare minimum of effort and experience. Game PCBs developed by these companies began soon after, with the few external manufacturers quickly following suit. Such it was that by the 1990s, the majority of arcade games and cabinets were built to JAMMA specifications.
JAMMA can be thought of in simplest terms as a specification that defines the various inputs and outputs required by a game PCB to interact with the controls, video, and sound in the arcade cabinet. The standard defines 56 specific inputs and outputs on the PCB, and their location on the connector "harness" that attaches the board to the rest of the machine:
JAMMA Pinout Diagram
The smaller section of the connector represents the pins required for power to the board (from the arcade power supply) in the form of several +5 volt pins (used for the integrated circuits (ICs) such as memory, as well as the microcontroller controlling the game), +12 volt pins (used on some boards for sound amplification), and -5 volt pins (used on a few boards for audio as well, to power operational amplifiers).
JAMMA Harness
The larger section of the connector is where the party is. The coin counter pins provide a means for a mechanical counter to be incremented within the machine (for the benefit of the machine owner/operator). The lock out coil pins control the lock outs which are features in many coin mechanisms, which prevent redirect inserted coins to the coin return when activated. The speaker (-) and (+) pins are the outputs for sound, and output a mono-channel signal. The video red, green, blue, and sync pins represent the outputs for a basic 15kHz analog video signal analogous to the IBM Color Graphics Adapter format (CGA) but without the color limitations. The tilt pin is used for a tilt sensor, to let the cabinet know when the player is getting a bit too handsy. The test pin attaches to a button used to virtually insert a coin (without incrementing the counter). The service pin is connected to a button which in most systems brings up the contents of the read only memory (ROM). The coin switch pins attach to the actual detector in the coin mechanism to increment the number of credits. The remainder of the pins attach to the human interface components of the board such as the joystick and buttons.
Original "The Simpsons" JAMMA PCB
Important to note is that the digital signals both into and out of the board are considered "active low". This means that their inactive state is when they are "seeing" the reference voltage on the board, and are considered "activated" when they are pulled to ground and "see" zero volts.
Knowing the inputs and outputs required to interface with a game PCB via the JAMMA standard tells us exactly what peripherals are needed within the cabinet, and by extension what signals need to be present on the game board.