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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: *high
reliability Reliability, reliable, or unreliable may refer to: Science, technology, and mathematics Computing * Data reliability (disambiguation), a property of some disk arrays in computer storage * Reliability (computer networking), a category used to des ...
*lower repair cycle times or constraints such as: *limited technician accessibility *cost of testing during manufacture 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: # reduces test-cycle duration # reduces the complexity of the test/probe setup, by reducing the number of I/O signals that must be driven/examined under tester control. Both lead to a reduction in hourly charges for automated test equipment (ATE) service.


Applications

BIST is commonly placed in
weapon A weapon, arm, or armament is any implement or device that is used to deter, threaten, inflict physical damage, harm, or kill. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime (e.g., murder), law ...
s,
avionics Avionics (a portmanteau of ''aviation'' and ''electronics'') are the Electronics, electronic systems used on aircraft. Avionic systems include communications, Air navigation, navigation, the display and management of multiple systems, and the ...
,
medical device A medical device is any device intended to be used for medical purposes. Significant potential for hazards are inherent when using a device for medical purposes and thus medical devices must be proved safe and effective with reasonable assura ...
s,
automotive electronics Automotive electronics are electronic systems used in vehicles, including engine management, ignition, radio, carputers, telematics, in-car entertainment systems, and others. Ignition, engine and transmission electronics are also found in tru ...
, complex machinery of all types, unattended machinery of all types, and
integrated circuit An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...
s.


Automotive

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.


Aviation

Almost all avionics now incorporate BIST. In avionics, the purpose is to isolate failing
line-replaceable unit A line-replaceable unit (LRU), lower line-replaceable unit (LLRU), line-replaceable component (LRC), or line-replaceable item (LRI) is a modular component of an airplane, ship or spacecraft (or any other manufactured device) that is designed to b ...
s, which are then removed and repaired elsewhere, usually in depots or at the
manufacturer Manufacturing is the creation or Production (economics), production of goods with the help of equipment, Work (human activity), labor, machines, tools, and chemical or biological processing or formulation. It is the essence of the secondary se ...
. Commercial aircraft only make money when they fly, so they use BIST to minimize the time on the ground needed for repair and to increase the level of safety of the system which contains BIST. Similar arguments apply to military aircraft. When BIST is used in flight, a fault causes the system to switch to an alternative mode or equipment that still operates. Critical flight equipment is normally duplicated, or redundant. Less critical flight equipment, such as entertainment systems, might have a "limp mode" that provides some functions.


Electronics


Integrated circuit manufacturing

Built-In-Self-Test is used to make faster, less-expensive
integrated circuit An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...
manufacturing tests. The IC has a function that verifies all or a portion of the internal functionality of the IC. In some cases, this is valuable to customers, as well. For example, a BIST mechanism is provided in advanced
fieldbus A fieldbus is a member of a family of industrial digital communication networks used for real-time distributed control. Fieldbus profiles are standardized by the International Electrotechnical Commission (IEC) as IEC 61784/61158. A complex autom ...
systems to verify functionality. At a high level this can be viewed similar to the PC
BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is a type of firmware used to provide runtime services for operating systems and programs and to perform hardware initialization d ...
's
power-on self-test A power-on self-test (POST) is a process performed by firmware or software routines immediately after a computer or other digital electronic device is powered on. POST processes may set the initial state of the device from firmware and detec ...
(POST) that performs a self-test of the
RAM Ram, ram, or RAM most commonly refers to: * A male sheep * Random-access memory, computer memory * Ram Trucks, US, since 2009 ** List of vehicles named Dodge Ram, trucks and vans ** Ram Pickup, produced by Ram Trucks Ram, ram, or RAM may also ref ...
and buses on power-up.


Computers

The typical personal computer tests itself at start-up because it's a very complex piece of machinery. Since it includes a computer, a computerized self-test was an obvious, inexpensive feature. Most modern computers, including
embedded system An embedded system is a specialized computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is e ...
s, have self-tests of their computer, memory and software.


Unattended machinery

Unattended machinery performs self-tests to discover whether it needs maintenance or repair. Typical tests are for temperature, humidity, bad communications, burglars, or a bad
power supply A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, electric current, current, and frequency to power ...
. For example, power systems or batteries are often under stress, and can easily overheat or fail. So, they are often tested. Often the communication test is a critical item in a remote system. One of the most common unattended system is the telephone concentrator box. This contains complex electronics to accumulate telephone lines or data and route it to a central switch. Telephone concentrators test for communications continuously, by verifying the presence of periodic data patterns called frames (See
SONET Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diodes ...
). Frames repeat about 8,000 times per second. Remote systems often have tests to
loop back Loopback (also written loop-back) is the routing of electronic signals or digital data streams back to their source without intentional processing or modification. It is primarily a means of testing the communications infrastructure. Loopback c ...
the communications locally, to test transmitter and receiver, and remotely, to test the communication link without using the computer or software at the remote unit. Where electronic loop-backs are absent, the software usually provides the facility. For example, IP defines a local address which is a software loopback (IP-Address 127.0.0.1, usually locally mapped to name "localhost"). Many remote systems have automatic reset features to restart their remote computers. These can be triggered by lack of communications, improper software operation or other critical events. Satellites have automatic reset, and add automatic restart systems for power and
attitude control Spacecraft attitude control is the process of controlling the orientation of a spacecraft (vehicle or satellite) with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, ...
, as well.


Medicine

Medical devices test themselves to assure their continued safety. Normally there are two tests. A POST will perform a comprehensive test. Then, a periodic test will assure that the device has not become unsafe since the POST. Safety-critical devices normally define a "safety interval", a period of time too short for injury to occur. The self test of the most critical functions normally is completed at least once per safety interval. The periodic test is normally a subset of the POST.


Military

One of the first computer-controlled BIST systems was in the U.S.'s Minuteman Missile. Using an internal computer to control the testing reduced the weight of cables and connectors for testing. The Minuteman was one of the first major weapons systems to field a permanently installed computer-controlled self-test.


Specializations

There are several specialized versions of BIST which are differentiated according to what they do or how they are implemented: * Programmable built-in self-test (pBIST) * Memory built-in self-test (mBIST) - e.g. with the Marinescu algorithm *
Logic built-in self-test Logic built-in self-test (or LBIST) is a form of built-in self-test (BIST) in which hardware and/or software is built into integrated circuits allowing them to test their own operation, as opposed to reliance on external automated test equipment. ...
(LBIST) * Analog and mixed-signal built-in self-test (AMBIST) * Continuous built-in self-test (CBIST, C-BIT) * Event-driven built-in self-test, such as the BIST done to an aircraft's systems after the aircraft lands. * Periodic built-in self-test (C-BIT/P-BIT) * Interrupt-driven built-in self-test (IBIST) or user/operator-initiated built-in self-test (I-BIT, or O-BIT) * Power-up built-in self-test (PupBIST, P-BIT) * Automatic built-in self-test (ABIST)


Specification

Engineers specify the requirements, design, implementation, and verification of the built-in self-test mechanism in a BIT (or BIST) specification. The specification defines:U.S. Department of Defense. (1988). *MIL-STD-2065: Built-In Test (BIT) Design Guide*. * BIT Modes required: PBIT, CBIT, IBIT * BIT Objectives: Fault detection, fault isolation, fault reporting * Performance Requirements: ** Fault coverage ** Detection time ** Isolation capability (e.g., to LRU or SRU level) ** Availability: When BIT must be active ** Trigger Mechanisms: Conditions for BIT executionBIT * Architecture and Design ** Functional architecture (data flow, control flow) ** Interfaces (hardware/software) ** Test point allocation ** Fault injection capability * BIT Execution and Reporting ** How test results are collected ** Fault logging mechanism ** Operator interface and status displays * BIT Test Coverage ** List of detectable faults per subsystem ** Level of diagnostic resolution * Verification and Validation ** BIT test procedures ** Test environments (e.g.,
simulation A simulation is an imitative representation of a process or system that could exist in the real world. In this broad sense, simulation can often be used interchangeably with model. Sometimes a clear distinction between the two terms is made, in ...
,
hardware-in-the-loop Hardware-in-the-loop (HIL) simulation, also known by various acronyms such as HiL, HITL, and HWIL, is a technique that is used in the development and testing of complex real-time embedded systems. HIL simulation provides an effective testing platf ...
) ** Pass/fail criteria * Maintenance and Support Considerations ** Diagnostic codes and fault isolation manuals ** Integration with maintenance systems


See also

*
Built-in test equipment Built-in test equipment (BITE) for avionics primarily refers to passive fault management and diagnosis equipment built into airborne systems to support maintenance processes. Built-in test equipment includes multimeter A multimeter (also know ...
*
Logic built-in self-test Logic built-in self-test (or LBIST) is a form of built-in self-test (BIST) in which hardware and/or software is built into integrated circuits allowing them to test their own operation, as opposed to reliance on external automated test equipment. ...
*
Embedded system An embedded system is a specialized computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is e ...
*
System engineering Systems engineering is an interdisciplinary field of engineering and engineering management that focuses on how to design, integrate, and manage complex systems over their Enterprise life cycle, life cycles. At its core, systems engineering uti ...
*
Safety engineering Safety engineering is an engineering Branches of science, discipline which assures that engineered systems provide acceptable levels of safety. It is strongly related to industrial engineering/systems engineering, and the subset system safety en ...
*
Watchdog timer A watchdog timer (WDT, or simply a ''watchdog''), sometimes called a ''computer operating properly timer'' (''COP timer''), is an electronic or software timer that is used to detect and recover from computer malfunctions. Watchdog timers are wide ...


References


External links


Hardware Diagnostic Self Tests


- A Brief general overview of the capabilities and benefits of BIST by Analog Devices. {{DEFAULTSORT:Built-In Self-Test Test equipment Integrated circuits Maintenance