Reset Button

[aricsdaddy]

Can someone explain (simply) how the reset button works (I need to hack it)?  I know it has 4 pins, but does anyone have a pinout for these because when I test them for continuity with a multimeter, it gives strange readings across all the pins.

Thanks, AD

[P]

Official Famicom schematic here and Enri's is here (scroll down to the CPU schematic).
Both shows just two pins, one GND and one that goes to the CPU's /RST pin with a 0.47 uF capacitor connected to the legs of the switch.
I guess if it has 4 legs that just means that each pair is bridged (use a multimeter to check which is which).

Note that this applies to the Famicom only. The NES also has it connected to the PPU's /RST pin and it therefore also resets the PPU (this is why you see garbage on the screen when resetting a Famicom but not when resetting a NES).

[aricsdaddy]

Thanks for the schematics and info.  One other quick question if you do not mind though.

Is the reset switch a Off and momentary On (connected), or a On (connected) and momentary open switch as the schematics look like the circuit is normally connected, and when the reset is pressed it opens the circuit.. 

Thanks

[famiac]

The bar over the letters "RST" means the signal is active when the voltage is low. The switch connects /RST to ground. So, the line is only active when the switch is pressed.

The switch must be a normally open (momentary On)

[P]

Yeah that's why I type it as "/RST" where the leading slash is supposed to indicate the overline (¯) used in electronics notation for "active low" signals or negation.

It kinda clashes with the normal use of slashes though, like with a terminal labeled, say "RD/WR", and the second one is active low resulting in double slashes "RD//WR".

Western Design Center uses "B" for "bar" after the signal name to indicate this in their current documents, so "/RST" would be written as "RSTB".
Other common notation includes using "!" or "~" commonly used for negation in programming languages: "!RST" or "~RST".

[aricsdaddy]

Thank you people.  This will help with a major hack I am working on.