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Game Control

Entry posted by DanBoris July 25, 2006

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I am hoping that I can get a little help figuring this section out. I am pretty good with digital analysis, but my transistor theory is a little (ok a lot) rusty. The purpose of this section is to control the game state. Here are the things that I do know about this circuit:

- When either /STOPG1 or /STOPG2 goes low, indicating that one of the score counters has reached the game ending score, the output of B3 (STOP G) will go high which stops the game. The high on STOP G will also set /ATRACT low, putting the game into Attract mode.

- When a coin is inserted, COIN SW is momentarily closed which takes /SRST low, resetting the score counters.

- Antenna is an external input that is used to detect a static shock to the machine. In theory is should prevent someone from shocking the machine into giving them a free game.

I would appreciate any help deciphering how the rest of this circuit works.

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supercat 125

Posted July 25, 2006

Q2 will turn on when its base is pulled low. This can occur either as a result of /SRST going low, or as a result of Q1 being on. Q1 will turn on when its base is pulled high. This will happen when Q2 is on UNLESS either inverter E4 is kicking out a low signal or the Antenna input is kicking out a high signal. If either of those things happens, Q1 will be turned off regardless of the state of Q2.

The 0.1 microfarad capacitors add a small delay to the switching on of Q1 and Q2, except that the Antenna input will switch off Q1 instantly.

In simplest form: Q1 and Q2 will be on when the game is being played, and off when it isn't. When either transistor is on, it will try to switch on the other. Some events start a game by switching on Q2; others end a game by switching off Q1.