Hacking the Xbox

32
Hacking the Xbox: An Introduction to Reverse Engineering
and treating one as the “sacrificial” box helps remove the psychological
barrier one might otherwise have about performing aggressive experiments
on the hardware.
This chapter will introduce you to the basics of reverse engineering, with
a focus on basic techniques, such as reading circuit boards to build an
intuition, and some coverage of intermediate techniques such as pattern
matching and recognizing basic design motifs.
Reading a Circuit Board
The first thing you see when you take the cover off of a typical electronic
device is the circuit board. Typically colored green or tan, this multilayer
sandwich of copper, glass fiber and epoxy contains an exact schematic
netlist within its traces. In other words, by following the traces, one can
determine exactly how every component is connected. The placement of
components and the layout of the traces also contains clues that can bring
insight into the designer’s thought process.
Circuit Board Basics
A typical circuit board consists of a few layers of patterned copper
separated by thin sheets of fiberglass impregnated with epoxy. The color
of a raw circuit board is whitish or tan with copper traces; however,
almost all circuit boards are coated with a thin polymer called the
soldermask that gives circuit boards their familiar green color. Molten
solder does not adhere to the soldermask, so during production excess
solder does not stick to the board and cause shorts. The soldermask has
openings for connections to components. These openings typically have a
silvery color from a thin plating of tin or solder that is applied to prevent
the copper from oxidizing and to enhance solderability.
On top of the soldermask is typically a layer of white lettering referred
to as the silkscreen. Each component on a circuit board has an outline and
a unique designator on the silkscreen layer. The designator enables people
to quickly associate a component on a circuit board with a component on
a schematic. You can use the designator to help guess the function of a
component based on the component naming scheme. Table 2-1 summarizes
the component naming scheme used in the Xbox.