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
Official Famicom schematic here (https://www.nesdev.org/wiki/File:Neswires.jpg) and Enri's is here (http://www43.tok2.com/home/cmpslv/Famic/Famic.htm) (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).
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
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)
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".
Thank you people. This will help with a major hack I am working on.