In this case, we assume that the circuit includes two faults: a short fault between Net2 and Net3, and an open fault on Net4. We will also assume that a short between two nets behaves as a wired-AND and an open fault behaves as a stuck-at-1 condition. To detect and isolate defects, the tester shifts the patterns shown in Figure 3 into the first boundary-scan register and applies these patterns to the inputs of the second device.
The standard accounts for the addition of device-specific instructions and registers that can be used to interact with additional IC capabilities.
More recently, embedded IC instrumentation—from instruments that measure voltage and current to devices that can execute high-speed test on the chip—has used the JTAG TAP as the access mechanism, providing new visibility into the IC and further expanding the scope of JTAG testing. The input values captured in the boundary-scan register of the second device are shifted out and compared to the expected values.
In this case, the results, underlined and marked in red on Net2, Net3, and Net4, do not match the expected values and the tester tags these nets as faulty. Sophisticated algorithms are used to automatically generate the minimal set of test vectors to detect, isolate, and diagnose faults to specific nets, devices, and pins.
Boundary-scan technology is commonly applied to product design, prototype debugging, and field service as depicted in Figure 4. The same test suite used to validate design testability can adapted and utilized for board bring-up, high-volume manufacturing test, troubleshooting and repairs, and even field service and reprogramming.
Figure 4. JTAG tools are used in all phases of the product life cycle. You can also obtain a copy of the IEEE We have received your request and would like to thank you for contacting us. We will get back to you as soon as possible.
May 23, by. What is JTAG? Request Technical Support. Complete the form below to request technical support. Select a product CPXI BSR — this is the main testing data register. It allows other devices in a circuit to be tested with minimal overhead.
The file contains details of the Boundary Scan configuration for the device. For more detail on each state, refer to the IEEE This instruction allows the testing of other devices in the JTAG chain without any unnecessary overhead. However, the device is left in its normal functional mode. During this instruction, the BSR can be accessed by a data scan operation to take a sample of the functional data entering and leaving the device.
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The first way, connection testing see next section gives good test coverage, particularly for short circuit faults. Where two JTAG enabled pins are meant to be connected the test will make sure one pin can be controlled by the other.
Where enabled pins are not meant to be connected they are tested for short circuit faults by driving one pin and checking that these values are not read on the other pins. XJTAG will automatically generate the vectors required to run a connection test based on the netlist of a board and JTAG information for the enabled devices.
In order to add this open circuit coverage it is necessary to communicate with the peripheral device from boundary scan on the enabled device. If communication can be verified, there cannot be an open circuit fault. This type of testing can be very simple, for example lighting an LED and asking an operator to verify it has activated, or more complex, for example writing data into the memory array of a RAM and reading it back.
The library files contain models for all types of non-JTAG devices from simple resistors and buffers to complex memory devices such as DDR3. Because boundary scan disconnects the control of the pins on JTAG devices from their functionality the same model can be used irrespective of the JTAG device controlling a peripheral. Most boards already contain JTAG headers for programming or debug so there are no extra design requirements. In order to run any boundary scan based testing it is necessary to have some information about the implementation of JTAG on the enabled devices on a board.
Not at all. One of the key benefits to boundary scan testing is that the only test hardware required is a JTAG controller.
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