As many know; I'm working on a Re-theme/Custom machine - Star Trek: The Mirror Universe.
http://pinside.com/pinball/forum/topic/star-trek-mirror-universe-pinball
Anyway; I'm going to be re-inventing the wheel here... IE I don't want to do an MP3 Trigger because I feel the cost doesn't justify the functionality. Instead; I plan on re-purposing a Raspberry Pi to do the Audio work for the switch positions. I've already done some initial software planning and can confirm that I can do up to 8 voices-at a time- using the RPi.
Anyway; I'm going to be using a Microchip MCP23017 I2C GPIO chip as a 16bit interface the 5x8 switch matrix on the Bally 6502 era machines. I want to directly connect to the switch matrix at A4J2 in the blackbox.
Can someone who's been spending a lot of time in this switch matrix tell me how it operates? I'm pretty sure that the MPU sends pulses to the Strobe signals (ST0-ST4) and that if a switch is closed... it causes that pulse to appear on the I0-I7 lines. What I don't know for sure is if the MPU is pulsing the signal active high or low.
Looking at the schematics; It would seem that in the absence of no signal; the strobes would float high given the 3.3k pullups behind the anode of the diodes. This would lead me to think that the pulse was active high but not sure as the software/code could be actively driving the stobes each cycle.
Would someone in the know wanna help a hacker out? IF you got a logic analyzer capture- that would be icing on the cake.