What is the Boundary Scan device Test Operation mode?

Boundary Scan test operation mode

During the boundary scan device test operation mode, a single boundary register cell routes input and output signals so the device's core logic essentially ignores the inputs and outputs. Only test signals are permitted to pass through the core logic (for INTEST, RUNBIST, and other self-tests) in this mode. This effectively isolates the device from the rest of the board.

While in test mode, you can execute EXTEST, INTEST, RUNBIST, and manufacturer-defined functions that emulate or extend these tests.

EXTEST checks the physical connections of the boundary-scan device.

INTEST and RUNBIST test the internal logic of the device.

Manufacturer-defined tests might require you to preset the cells in the boundary register (PRELOAD) so the states will be known when the test mode is entered. Check to see if your devices or board topology have such a requirement before writing your test.

Figure 1 illustrates the status of the boundary register cells during test operation mode. The black lines show how data is routed during test mode. The red lines show how data is shifted out of the cell; this is the path taken during EXTEST. The green lines show the path for updating data; this is the path taken during INTEST.

        Figure 1. Cell status during test operation mode