Hacking the Xbox

Chapter 8 - Reverse Engineering Xbox Security 125
into a 50 ohm load. Also, CMOS transmitters should have no problem
driving a wire terminated into a fixed voltage. Thus, a standard LVDS to
CMOS converter chip can be used to take the Xbox motherboard’s
HyperTransport signals and feed them into the board I had previously built
for my thesis. The chip I chose was the Texas Instruments SN65LVDS386,
and you can find data sheets for this chip at Texas Instruments’ website.
Attaching the LVDS-to-CMOS converter chip to the board is made
delightfully simple by the clean layout used for the HyperTransport bus on
the Xbox motherboard. Figure 8-1 is a picture of what the HyperTransport
bus traces look like. Notice how all the wires run in parallel and how they are
evenly spaced. Some of the wires, such as the clock (TX CK/TX CX* and RX
CK/RX CX*) and the strobe line (TXD8/TXD8* and RXD8/RXD8*), are
even labeled for us with polarity markings! This simple layout enables the
use of an easy-to-engineer tap board.
The tap board contains just the LVDS-to-CMOS converter chip, some
power conditioning circuitry, and a set of traces laid out right up to the edge
of the board that are identically spaced to the HyperTransport bus on the
Xbox motherboard. For identical spacing and easy alignment and mounting,
I measured the dimensions of these traces using a digital caliper tool.
Figure 8-2 illustrates the dimensions of the HyperTransport bus traces.
Figure 8-1: HyperTransport bus traces as laid out on an Xbox motherboard.