Talk:CPU pinout

Pin 30

The signal from pin 30 goes through the exact same "processing" as the chip's /RESET signal, at which point it goes to the output logic for the M2 pin (don't know exactly what it does) and then through an inverter which goes to the enables for $4018-$401A and to some other spots (seemingly related to the data buffer used for Sprite DMA). Bit 7 of the writable register at $401A seems to propagate to numerous locations within the sound channels and thus might be responsible for the observation of all writable registers disappearing. --Quietust 16:49, 29 April 2011 (UTC)

When pin 30's input is "processed" it gets inverted, just like with the /RESET pin (since transistors themselves are active-high) - that signal then gets inverted again (so it's now equal to pin 30's input, normalized) and NORed together with the inverted +RESET signal (so it's also the actual state of the input signal), and that result goes to the M2 pin's output logic; thus, the M2 pin will only respond to RESET (in whatever way that is - I haven't traced that part yet, but it's most likely turning off the output drivers and going high impedance) when pin 30 is also low. --Quietust 19:45, 7 May 2011 (UTC)