Hacking the Xbox

Chapter 1 - Voiding the Warranty 19
For basic modification and kit-build projects, DMMs are useful for
checking for shorted connections, and for checking the basic health of a
circuit before and after applying power. Continuity mode in a DMM can
be helpful when you feel like you may have messed up a solder connection.
In continuity mode, the DMM will emit a tone whenever a low-resistance
path exists between the test probes. Thus, the continuity feature is useful
for both verifying the integrity of a solder joint, and for checking for
shorts with adjacent connections. You should not use continuity mode to
check for power supply shorts, because some boards will quite normally
have a sufficiently low resistance between power and ground (ten ohms
or so) to trigger the continuity tone. Thus, before applying power to any
newly modified or built board, use the resistance measuring mode to
check and make sure that there is no dead short (zero ohms of resistance)
on the power lines.
For reverse engineering and more advanced projects, the basic tools
you’ll need are an oscilloscope and sometimes a logic analyzer. Oscilloscopes
are useful for capturing the detailed shape of electrical waveforms.
One can diagnose timing, noise and interference problems with an
oscilloscope.
The oscilloscope’s basic defining characteristics are the number of
channels or waveforms it can display simultaneously, and its maximum
electrical bandwidth. High-quality oscilloscopes typically have four
channels and over 500 MHz of bandwidth; discount or used oscilloscopes
often have only two channels and somewhere between 20 MHz
and 100 MHz of usable bandwidth. The chief limitation of all oscilloscopes
is that they can only display a short segment of an electrical
waveform.
Logic analyzers are useful for capturing large quantities of digital data.
They trade off the ability to capture waveform shape for expansive data
analysis and logging capabilities. Logic analyzers are useful for diagnosing
complex digital busses and circuits. The basic defining characteristics of a
logic analyzer are the number of digital channels it can sample, the
maximum sampling rate, and the maximum sampling depth. A typical
modern logic analyzer may have several dozen channels, a sampling rate
in the hundreds of megahertz, and a sampling depth of a couple megabytes.
Other features found in logic analyzers are programmable trigger
algorithms and the ability to detect glitches or runt pulses.
Unfortunately, the average price of a new oscilloscope or logic analyzer
runs in the thousands to tens of thousands of dollars. The good news is
that most projects will not require the latest and greatest in test technology,
so you can get away with second-hand equipment. Swapfests are
great places to pick up an old scope or analyzer for cheap; eBay also has
some good deals from time to time. If you have to make a choice
between purchasing an oscilloscope and a logic analyzer, I’d recommend
getting the oscilloscope first; a logic analyzer is not nearly as versatile as