What is JTAG and how can I make use of it?
XJTAG – Experts in JTAG / Boundary Scan
Eight reasons why you should use
XJTAG to test your boards
Three simple letters – BGA One tool for test and programming
An increasing number of devices are supplied in BGA
(Ball Grid Array) packaging. Each BGA device on a board
imposes severe restrictions on the testing that can be done
using traditional bed-of-nails or flying probe machines. JTAG is often already used as one step in production:
programming. By also using JTAG for boundary scan test
it is possible to reduce the number of steps and handling
operations in the production process.
Using a simple four-pin interface, JTAG / boundary scan
allows the signals on enabled devices to be controlled
and monitored without any direct physical access.
Three more letters – NRE
The non-recurring engineering (NRE) costs of building test
fixtures can be prohibitively high. In many cases using
JTAG / boundary scan will remove the need for such a
fixture, in other cases the fixture can be dramatically
simplified resulting in significant cost savings.
Production level tests on the engineer’s
bench for prototype boards
Traditional test technologies require very large and
expensive equipment. The only test equipment required
for JTAG / boundary scan testing is a JTAG controller –
XJTAG’s XJLink2 controller is a similar size to a PC mouse.
Excellent fault diagnostics
Identified short
Shorter test times
For boards with low production volumes it has always
been difficult to justify the cost of test fixture development.
In these cases one alternative is flying probe testing;
however the test cycle times tend to be high for this
technology. JTAG / boundary scan test gives fast test
times with no need for a costly fixture.
Lower test development costs
As different processors / FPGAs interact with
peripherals in different ways, traditional functional test
requires costly custom development for each board.
JTAG / boundary scan significantly reduces such
development costs because it provides a simplified
interface to control the IO pins used to interact with
peripherals. This standard interface, which is the same
for all JTAG enabled devices, means a generic set of
test models can be used, and re-used, when building
test systems.
JTAG / boundary scan, unlike
functional test, provides high
precision fault information to
help with rapid repair. XJTAG
also provides the capability
to view both the physical
location of a fault on the
layout of the board and the
logical design of the area of
the circuit in which the fault
exists on the schematic.
Most likely short locations
Recover ‘dead’ boards
where functional test would not work
XJTAG boundary scan tests can be run on any board
with a working JTAG interface. Traditional functional tests
cannot be run if the board does not boot; simple faults
on key peripherals, such as RAM or clocks, would be
found using JTAG but would prevent functional tests
from providing any diagnostic information.
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