Hardware/MX23L4005

Much as with the GameCube, the MX "RTC-SRAM-ROM" chip sits on the EXI bus at address 0-1. http://hitmen.c02.at/files/yagcd/yagcd/chap10.html#sec10.3

Dieshot courtesy of Flylogic

Font data

The only data contained in ROM on the Wii is two fontsets (one Latin, on Japanese). They are compressed using a proprietary format (Yay0), and generally only used in GameCube mode.

RTC

Real-Time Clock (RTC) is 32-bit value, counting time intervals in seconds. To get the real time (seconds since January 1st, 2000 12am) add the counter bias saved in SRAM (or is it stored in NAND? ^[check])

SRAM

The SRAM stores some miscellaneous settings that are only used in GameCube compatibility mode.

The custom MX23L4005 chip used on the Nintendo Wii contains the GameCube font set, RTC, and power management functions. It is listed on WiiRe as "U8: MX "E062674-MG" "MX23L4005-24C1" "RTC-RVL A" "2S08802" (RTC, TSOP28 18x8mm)".

Die shot: http://www.bunniestudios.com/blog/?p=227

Observed pin behavior:

1 connected to power button - active high (measures +3.3v while power button is pressed)
2 wii power state (+3.3v when power is on or in standby, 0v otherwise) TP113 comes on slightly after pin 3
3 wii power state (+3.3v when power is on or in standby, 0v otherwise) (nc on PCB!)
4 Gnd
5 0? TP46 pulses occasionally to 1
6 1? TP106 green LED?
7 0? TP45

8 0?  measuring this pin prevents the wii from shutting off when you hold the power button down ?!!?
9 nc on PCB
10 TP109 0?
11 TP43 0?
12 TP44 exi?
13 TP41 exi?
14 TP42 exi?

15 exi?
16 Gnd
17 3.3v when wii has power applied
18 3.3v when wii has power applied
19 TP108 measuring this causes wii to power on immediately
20 TP231 0? 
21 TP110 3.3v when wii has power applied, goes low briefly when powering off

22 xtal
23 xtal
24 TP119 turns on shortly after poweron (connects to U10)
25 TP117 +3.3v when wii has power (connects to U9)
26 TP116 0?
27 +3.3v when wii has power
28 NC on PCB