
General product design 307
probe. If the test input is set, the program jumps to the test routines rather than to the
main operating routines. These are arranged to exercise all inputs, outputs and control
signals continuously in a predictable manner, so that the test equipment can monitor
them for the correct function. The test software operation depends of course on the core
functions of the microprocessor, and its bus and control signal interconnections, being
fault-free.
More complex digital systems cannot easily be tested or, more to the point,
debugged, with the techniques described so far. The boundary scan methods described
in section 9.3.3 ...