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49-499: FlexRay is a communication bus designed to ensure high data rates, fault tolerance, operating on a time cycle, split into static and dynamic segments for event-triggered and time-triggered communications. It is mainly used in aeronautic and automotive sectors. FlexRay supports data rates up to 10 Mbit/s , explicitly supports both star and bus physical topologies, and can have two independent data channels for fault-tolerance (communication can continue with reduced bandwidth if one channel

98-522: A binit as an arbitrary information unit equivalent to some fixed but unspecified number of bits. Logic analyzers A logic analyzer is an electronic instrument that captures and displays multiple logic signals from a digital system or digital circuit . A logic analyzer may convert the captured data into timing diagrams , protocol decodes, state machine traces, opcodes , or may correlate opcodes with source-level software. Logic analyzers have advanced triggering capabilities, and are useful when

147-409: A byte or word , is referred to, it is usually specified by a number from 0 upwards corresponding to its position within the byte or word. However, 0 can refer to either the most or least significant bit depending on the context. Similar to torque and energy in physics; information-theoretic information and data storage size have the same dimensionality of units of measurement , but there

196-509: A unit of information , the bit is also known as a shannon , named after Claude E. Shannon . The symbol for the binary digit is either "bit", per the IEC 80000-13 :2008 standard, or the lowercase character "b", per the IEEE 1541-2002 standard. Use of the latter may create confusion with the capital "B" which is the international standard symbol for the byte. The encoding of data by discrete bits

245-482: A Bell Labs memo on 9 January 1947 in which he contracted "binary information digit" to simply "bit". A bit can be stored by a digital device or other physical system that exists in either of two possible distinct states . These may be the two stable states of a flip-flop , two positions of an electrical switch , two distinct voltage or current levels allowed by a circuit , two distinct levels of light intensity , two directions of magnetization or polarization ,

294-429: A bit was represented by the polarity of magnetization of a certain area of a ferromagnetic film, or by a change in polarity from one direction to the other. The same principle was later used in the magnetic bubble memory developed in the 1980s, and is still found in various magnetic strip items such as metro tickets and some credit cards . In modern semiconductor memory , such as dynamic random-access memory ,

343-507: A digital system. Later, specialized connectors came into use. The evolution of logic analyzer probes has led to a common footprint that multiple vendors support, which provides added freedom to end users. Introduced in April, 2002, connectorless technology (identified by several vendor-specific trade names: Compression Probing; Soft Touch; D-Max) has become popular. These probes provide a durable, reliable mechanical and electrical connection between

392-481: A previously recorded data set, and halt capture or visually notify the operator when this data set is either matched or not. This is useful for long-term empirical testing. Recent analyzers can even be set to email a copy of the test data to the engineer on a successful trigger. Many digital designs, including those of ICs , are simulated to detect defects before the unit is constructed. The simulation usually provides logic analysis displays. Often, complex discrete logic

441-404: A time in serial transmission , and by a multiple number of bits in parallel transmission . A bitwise operation optionally processes bits one at a time. Data transfer rates are usually measured in decimal SI multiples of the unit bit per second (bit/s), such as kbit/s. In the earliest non-electronic information processing devices, such as Jacquard's loom or Babbage's Analytical Engine , a bit

490-436: A user needs to see the timing relationships between many signals in a digital system. Presently, there are three distinct categories of logic analyzers available on the market: A logic analyzer can be triggered on a complicated sequence of digital events, then capture a large amount of digital data from the system under test (SUT). When logic analyzers first came into use, it was common to attach several hundred "clips" to

539-486: Is in general no meaning to adding, subtracting or otherwise combining the units mathematically, although one may act as a bound on the other. Units of information used in information theory include the shannon (Sh), the natural unit of information (nat) and the hartley (Hart). One shannon is the maximum amount of information needed to specify the state of one bit of storage. These are related by 1 Sh ≈ 0.693 nat ≈ 0.301 Hart. Some authors also define

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588-415: Is inoperative). The bus operates on a time cycle, divided into two parts: the static segment and the dynamic segment. The static segment is preallocated into slices for individual communication types, providing stronger determinism than its predecessor CAN . The dynamic segment operates more like CAN, with nodes taking control of the bus as available, allowing event-triggered behavior. The FlexRay Consortium

637-554: Is more compressed—the same bucket can hold more. For example, it is estimated that the combined technological capacity of the world to store information provides 1,300 exabytes of hardware digits. However, when this storage space is filled and the corresponding content is optimally compressed, this only represents 295 exabytes of information. When optimally compressed, the resulting carrying capacity approaches Shannon information or information entropy . Certain bitwise computer processor instructions (such as bit set ) operate at

686-416: Is verified by simulating inputs and testing outputs using boundary scan . Logic analyzers can uncover hardware defects that are not found in simulation. These problems are typically too difficult to model in simulation, or too time-consuming to simulate and often cross multiple clock domains. Field-programmable gate arrays have become a common measurement point for logic analyzers and are also used to debug

735-434: The bus . Each bit to be sent is held on the bus for 8 sample clock cycles. The receiver keeps a buffer of the last 5 samples, and uses the majority of the last 5 samples as the input signal. Single-cycle transmission errors may affect results near the boundary of the bits, but will not affect cycles in the middle of the 8-cycle region. The value of the bit is sampled in the middle of the 8-bit region. The errors are moved to

784-410: The yottabit (Ybit). When the information capacity of a storage system or a communication channel is presented in bits or bits per second , this often refers to binary digits, which is a computer hardware capacity to store binary data ( 0 or 1 , up or down, current or not, etc.). Information capacity of a storage system is only an upper bound to the quantity of information stored therein. If

833-449: The 1940s, computer builders experimented with a variety of storage methods, such as pressure pulses traveling down a mercury delay line , charges stored on the inside surface of a cathode-ray tube , or opaque spots printed on glass discs by photolithographic techniques. In the 1950s and 1960s, these methods were largely supplanted by magnetic storage devices such as magnetic-core memory , magnetic tapes , drums , and disks , where

882-485: The 1960s, new and difficult problems began to arise, problems that oscilloscopes had trouble handling. For the first time in computing history, it became essential to simultaneously view large numbers of signals. Early solutions attempted to combine hardware from multiple oscilloscopes into one package, but screen clutter, a lack of definite data interpretation, as well as probing constraints made this solution only marginally usable. The HP 5000A Logic Analyzer, introduced in

931-652: The October 1973 issue of the Hewlett-Packard Journal , was probably the first commercially available instrument to be called a "Logic Analyzer". However, the HP 5000A was limited to two channels and presented information by means of two rows of 32 LEDs . The first truly parallel instrument was the twelve channel HP 1601L, it was a plug-in for the HP 180 series oscilloscope mainframes and used the oscilloscope screen to present 16 rows of 12 bit words as 1s and 0s. It

980-551: The TCP/IP stack and triggering on a certain HTTP packet). At this point, the user sets the analyzer to "run" mode, either triggering once, or repeatedly triggering. Once the data are captured, they can be displayed several ways, from the simple (showing waveforms or state listings) to the complex (showing decoded Ethernet protocol traffic). Some analyzers can also operate in a "compare" mode, where they compare each captured data set to

1029-409: The ambiguity of relying on the underlying hardware design, the unit octet was defined to explicitly denote a sequence of eight bits. Computers usually manipulate bits in groups of a fixed size, conventionally named " words ". Like the byte, the number of bits in a word also varies with the hardware design, and is typically between 8 and 80 bits, or even more in some specialized computers. In

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1078-424: The average. This principle is the basis of data compression technology. Using an analogy, the hardware binary digits refer to the amount of storage space available (like the number of buckets available to store things), and the information content the filling, which comes in different levels of granularity (fine or coarse, that is, compressed or uncompressed information). When the granularity is finer—when information

1127-441: The clock drift is no larger than 1 per 300 cycles, the drift may skew the clock no more than 1 cycle. Small transmission errors during the receiving may affect only the boundary bits. So in the worst case the two middle bits are correct, and thus the sampled value is correct. Here's an example of a particularly bad case - error during synchronization, a lost cycle due to clock drift and error in transmission. Errors that happened in

1176-415: The early 21st century, retail personal or server computers have a word size of 32 or 64 bits. The International System of Units defines a series of decimal prefixes for multiples of standardized units which are commonly also used with the bit and the byte. The prefixes kilo (10 ) through yotta (10 ) increment by multiples of one thousand, and the corresponding units are the kilobit (kbit) through

1225-494: The example: Despite so many errors, the communication was received correctly. The green cells are sampling points. All except the first are synchronized by the 1->0 edge in the transmission fragment shown. When developing and/or troubleshooting the FlexRay bus, examination of hardware signals can be very important. Logic analyzers and bus analyzers are tools which collect, analyze, decode, store signals so people can view

1274-501: The extreme cycles, and the clock is synchronized frequently enough for the drift to be small. (Drift is smaller than 1 cycle per 300 cycles, and during transmission the clock is synchronized more than once every 300 cycles.) All the communication is sent in the form of frames. The message consists of bytes { x 0 , x 1 , … , x m − 1 } {\displaystyle \{x_{0},x_{1},\dots ,x_{m-1}\}} , packed in

1323-512: The following way: If nothing is being communicated, the bus is held in state 1 (high voltage), so every receiver knows that the communication started when the voltage drops to 0. The receiver knows when the message is complete by checking whether BSS0 (1) or FES (0) was received. Note that 8-cycle per bit has nothing to do with bytes. Each byte takes 80 cycles to transfer. 16 for BSS0 and BSS1 and 64 for its bits. Also note that BSS0 has value 1, and BSS1 has value 0. Clocks are resynchronized when

1372-590: The high-speed waveforms at their leisure. Ethernet may replace FlexRay for bandwidth intensive, non-safety critical applications. Megabit The bit is the most basic unit of information in computing and digital communication . The name is a portmanteau of binary digit . The bit represents a logical state with one of two possible values . These values are most commonly represented as either " 1 " or " 0 " , but other representations such as true / false , yes / no , on / off , or + / − are also widely used. The relation between these values and

1421-409: The level of manipulating bits rather than manipulating data interpreted as an aggregate of bits. In the 1980s, when bitmapped computer displays became popular, some computers provided specialized bit block transfer instructions to set or copy the bits that corresponded to a given rectangular area on the screen. In most computers and programming languages, when a bit within a group of bits, such as

1470-469: The logic circuit. Logic Analyzers are also very useful when it comes to analyze serial protocols, like I2C , SPI or UART , as they allow to capture long logic sequences showing one or several communication frames. Usually, the Logic Analyzer software will also interpret the protocol layer, making debugging of firmware less tedious task. As digital computing and integrated circuits emerged in

1519-408: The orientation of reversible double stranded DNA , etc. Bits can be implemented in several forms. In most modern computing devices, a bit is usually represented by an electrical voltage or current pulse, or by the electrical state of a flip-flop circuit. For devices using positive logic , a digit value of 1 (or a logical value of true) is represented by a more positive voltage relative to

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1568-443: The physical states of the underlying storage or device is a matter of convention, and different assignments may be used even within the same device or program . It may be physically implemented with a two-state device. A contiguous group of binary digits is commonly called a bit string , a bit vector, or a single-dimensional (or multi-dimensional) bit array . A group of eight bits is called one  byte , but historically

1617-435: The probe and the circuit board with less than 0.5 to 0.7 pF loading per signal. Once the probes are connected, the user programs the analyzer with the names of each signal, and can group several signals together for easier manipulation. Next, a capture mode is chosen, either "timing" mode, where the input signals are sampled at regular intervals based on an internal or external clock source, or "state" mode, where one or more of

1666-517: The representation of 0 . Different logic families require different voltages, and variations are allowed to account for component aging and noise immunity. For example, in transistor–transistor logic (TTL) and compatible circuits, digit values 0 and 1 at the output of a device are represented by no higher than 0.4 V and no lower than 2.6 V, respectively; while TTL inputs are specified to recognize 0.8 V or below as 0 and 2.2 V or above as 1 . Bits are transmitted one at

1715-451: The sender there will be between 299 and 301 cycles of the receiver. The clocks are resynchronized frequently enough to assure that this causes no problems. The clock is sent in the static segment. Correct averaging in case of no errors. The signal is merely delayed by 2 cycles. Errors near the middle of 8-cycle region are canceled. Errors near the boundary of 8-cycle region may affect the boundary bit. At each time, only one ECU writes to

1764-417: The signals are defined as "clocks", and data are taken on the rising or falling edges of these clocks, optionally using other signals to qualify these clocks. After the mode is chosen, a trigger condition must be set. A trigger condition can range from simple (such as triggering on a rising or falling edge of a single signal) to the very complex (such as configuring the analyzer to decode the higher levels of

1813-424: The size of the byte is not strictly defined. Frequently, half, full, double and quadruple words consist of a number of bytes which is a low power of two. A string of four bits is usually a nibble . In information theory , one bit is the information entropy of a random binary variable that is 0 or 1 with equal probability, or the information that is gained when the value of such a variable becomes known. As

1862-577: The thickness of alternating black and white lines. The bit is not defined in the International System of Units (SI). However, the International Electrotechnical Commission issued standard IEC 60027 , which specifies that the symbol for binary digit should be 'bit', and this should be used in all multiples, such as 'kbit', for kilobit. However, the lower-case letter 'b' is widely used as well and

1911-556: The two possible values of one bit of storage are not equally likely, that bit of storage contains less than one bit of information. If the value is completely predictable, then the reading of that value provides no information at all (zero entropic bits, because no resolution of uncertainty occurs and therefore no information is available). If a computer file that uses n  bits of storage contains only m  <  n  bits of information, then that information can in principle be encoded in about m  bits, at least on

1960-444: The two values of a bit may be represented by two levels of electric charge stored in a capacitor . In certain types of programmable logic arrays and read-only memory , a bit may be represented by the presence or absence of a conducting path at a certain point of a circuit. In optical discs , a bit is encoded as the presence or absence of a microscopic pit on a reflective surface. In one-dimensional bar codes , bits are encoded as

2009-409: The voted signal changes from 1 to 0, if the receiver was in either idle state or expecting BSS1. As synchronization is done on the voted signal, small transmission errors during synchronization that affect the boundary bits may skew the synchronization no more than 1 cycle. As there are at most 88 cycles between synchronization (BSS1, 8 bits of the last byte, FES and TES - 11 bits of 8 cycles each), and

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2058-451: Was also used in Morse code (1844) and early digital communications machines such as teletypes and stock ticker machines (1870). Ralph Hartley suggested the use of a logarithmic measure of information in 1928. Claude E. Shannon first used the word "bit" in his seminal 1948 paper " A Mathematical Theory of Communication ". He attributed its origin to John W. Tukey , who had written

2107-433: Was introduced in 2008 in the new BMW 7 Series (F01) . The FlexRay system consists of a bus and electronic control units (ECUs). Each ECU has an independent clock. The clock drift must be not more than 0.15% from the reference clock, so the difference between the slowest and the fastest clock in the system is no greater than 0.3%. This means that, if ECU-s is a sender and ECU-r is a receiver, then for every 300 cycles of

2156-517: Was introduced in the January 1974 Hewlett-Packard Journal . Mixed-signal oscilloscopes combine the functionality of a digital storage oscilloscope with a logic analyzer. The several benefits of these include the ability to view analog and digital signals together in time, and to trigger on either digital or analog signals and capture on the other. A few limitations of mixed signal oscilloscopes are that they do not capture state-mode data, they have

2205-482: Was made up of the following core members: There were also Premium Associate and Associate members of FlexRay consortium. By September 2009, there were 28 premium associate members and more than 60 associate members. At the end of 2009, the consortium disbanded. The first series production vehicle with FlexRay was at the end of 2006 in the BMW X5 (E70) , enabling a new and fast adaptive damping system. Full use of FlexRay

2254-460: Was often stored as the position of a mechanical lever or gear, or the presence or absence of a hole at a specific point of a paper card or tape . The first electrical devices for discrete logic (such as elevator and traffic light control circuits , telephone switches , and Konrad Zuse's computer) represented bits as the states of electrical relays which could be either "open" or "closed". When relays were replaced by vacuum tubes , starting in

2303-507: Was recommended by the IEEE 1541 Standard (2002) . In contrast, the upper case letter 'B' is the standard and customary symbol for byte. Multiple bits may be expressed and represented in several ways. For convenience of representing commonly reoccurring groups of bits in information technology, several units of information have traditionally been used. The most common is the unit byte , coined by Werner Buchholz in June 1956, which historically

2352-541: Was used in the punched cards invented by Basile Bouchon and Jean-Baptiste Falcon (1732), developed by Joseph Marie Jacquard (1804), and later adopted by Semyon Korsakov , Charles Babbage , Herman Hollerith , and early computer manufacturers like IBM . A variant of that idea was the perforated paper tape . In all those systems, the medium (card or tape) conceptually carried an array of hole positions; each position could be either punched through or not, thus carrying one bit of information. The encoding of text by bits

2401-405: Was used to represent the group of bits used to encode a single character of text (until UTF-8 multibyte encoding took over) in a computer and for this reason it was used as the basic addressable element in many computer architectures . The trend in hardware design converged on the most common implementation of using eight bits per byte, as it is widely used today. However, because of

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