Built-in self-test (BIST)

Built-in self-test puts the tester inside the chip. Instead of an expensive external machine feeding patterns and checking responses, BIST adds a small on-chip pattern generator and a response analyzer so a block can test itself: you assert a 'start test' pin, the chip runs, and it raises a single pass/fail flag. It is the difference between mailing your watch to a lab versus the watch having a self-diagnostic button.

The most common kind is MBIST (memory BIST), because on-chip SRAMs are dense, defect-prone, and hard to reach through scan; a tiny finite-state machine marches algorithmic patterns (like the classic 'March' tests) through every memory cell and flags any that misbehave. Logic BIST (LBIST) uses a pseudo-random pattern generator (an LFSR) feeding scan chains, with a MISR compacting the outputs into a single signature compared against a golden value. BIST shines for in-field and power-on self-test — a car's brake controller can re-test itself every time you start the engine — and reduces dependence on slow, costly external testers.