Built-in self-test

A built-in self-test (BIST) or built-in test (BIT) is a mechanism that permits a machine to test itself. Engineers design BISTs to meet requirements such as:

or constraints such as:

The main purpose of BIST is to reduce the complexity, and thereby decrease the cost and reduce reliance upon external (pattern-programmed) test equipment. BIST reduces cost in two ways:

Both lead to a reduction in hourly charges for automated test equipment (ATE) service.

The BIST name and concept originated with the idea of including a pseudorandom number generator (PRNG) and cyclic redundancy check (CRC) on the IC. If all the registers that hold state in an IC are on one or more internal scan chains, then the function of the registers and the combinational logic between them will generate a unique CRC signature over a large enough sample of random inputs. So all an IC need do is store the expected CRC signature and test for it after a large enough sample set from the PRNG. The CRC comparison with expected signature or the actual resultant CRC signature is typically accessed via the JTAG IEEE 1149.1 standard.

BIST is commonplace in weapons, avionics, medical devices, automotive electronics, complex machinery of all types, unattended machinery of all types, and integrated circuits.

Automotive tests itself to enhance safety and reliability. For example, most vehicles with antilock brakes test them once per safety interval. If the antilock brake system has a broken wire or other fault, the brake system reverts to operating as a normal brake system. Most automotive engine controllers incorporate a "limp mode" for each sensor, so that the engine will continue to operate if the sensor or its wiring fails. Another, more trivial example of a limp mode is that some cars test door switches, and automatically turn lights on using seat-belt occupancy sensors if the door switches fail.

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