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February, 2020


Eight reasons why you should use XJTAG to test your boards


Three simple letters – BGA


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.


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 scanwill remove the need for such a fixture, in other cases the fixture can be dramatically simplified resulting in significant cost savings.


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 such development test requires costly


custom development for each board. JTAG / boundary scan significantly reduces


costs because it


provides a simplified interface to control the I/O 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.


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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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.


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 JTAG /


functional


boundary test,


scan, provides


unlike 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


Identified short


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