Hacking the Xbox

Tip
Chapter 2 - Thinking Inside the Box 33
The Xbox motherboard includes a handy coordinate system
printed along the edges of the board in the silkscreen
layer. On the component side of the board, the coordinates
go from A through G on the sides, and from 1 through 8
along the top and bottom. The reverse side of the board
has coordinates M through V along the sides. Note that the
letters I, O, Q, and S are skipped because they can be confused
with the numbers 0, 1, and 5. Component designators
on the Xbox motherboard are encoded using this coordinate
system; thus, J7D1, the LPC debug port, can be found
on the top side at coordinates 7D. This book will frequently
use this coordinate system along with the component designators
to refer to specific components.
Connections between wiring layers are made by copper-filled holes called vias.
Since the cost of a circuit board grows with the number of layers, most
consumer electronic devices are designed to keep the number of layers to a
minimum. Radio receivers and audio amplifiers will typically use singlesided
boards, whereas the latest PC motherboards might have up to six or
eight layers. The Xbox motherboard has four layers. The top two layers are
dedicated to carrying information between chips, and the inner two layers are
dedicated to delivering power. The Xbox motherboard will appear opaque
at first glance because the inner power layers are basically solid sheets of
copper. The good news for reverse engineering is that we can trace every
connection on the Xbox motherboard through casual visual inspection
because all of the signals layers are outside of the opaque power layers. The
Xbox design contrasts with motherboards that bury two or four signal
layers inside of the power layers. Buried signal layers can make signal
tracing difficult. (Note that the decision to bury signals inside power
Designator Component Type
C Capacitor
R Resistor
U Integrated Circuit or Transistor
L Inductor
RP Resistor Pack
Q Transistor
CR Diode
J Connector or Jumper
RT Resettable Fuse
Y Crystal
Table 2-1: The Xbox component naming scheme.