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56-515: IEEE 1284 , also known as the Centronics port , is a standard that defines bi-directional parallel communications between computers and other devices. It was originally developed in the 1970s by Centronics before its IEEE standardization. In the 1970s, Centronics developed the now-familiar printer parallel port that soon became a de facto standard . Centronics had introduced the first successful low-cost seven-wire print head, which used

112-431: A byte ) simultaneously, whereas a serial channel would convey those same bits sequentially, one at a time. If both channels operated at the same clock speed , the parallel channel would be eight times faster. A parallel channel may have additional conductors for other signals, such as a clock signal to pace the flow of data, a signal to control the direction of data flow, and handshaking signals. Parallel communication

168-462: A "low" and between 2.4 V and V CC for a "high", providing at least 0.4 V of noise immunity . Standardization of the TTL levels is so ubiquitous that complex circuit boards often contain TTL chips made by many different manufacturers selected for availability and cost, compatibility being assured. Two circuit board units off the same assembly line on different successive days or weeks might have

224-523: A SCSI HBA years ago. One huge advantage of having fewer wires/pins in a serial cable is the significant reduction in the size, the complexity of the connectors, and the associated costs. Designers of devices such as smartphones benefit from the development of connectors/ports that are small, durable, and still provide adequate performance. On the other hand, there has been a resurgence of parallel data links in RF communication. Rather than transmitting one bit at

280-432: A different mix of brands of chips in the same positions on the board; repair is possible with chips manufactured years later than original components. Within usefully broad limits, logic gates can be treated as ideal Boolean devices without concern for electrical limitations. The 0.4 V noise margins are adequate because of the low output impedance of the driver stage, that is, a large amount of noise power superimposed on

336-406: A few hundred transistors each. Functions within a single package generally range from a few logic gates to a microprocessor bit-slice . TTL also became important because its low cost made digital techniques economically practical for tasks previously done by analog methods. The Kenbak-1 , ancestor of the first personal computers , used TTL for its CPU instead of a microprocessor chip, which

392-420: A form of surface-mount package, with leads suitable for welding or soldering to printed circuit boards. Today , many TTL-compatible devices are available in surface-mount packages, which are available in a wider array of types than through-hole packages. TTL is particularly well suited to bipolar integrated circuits because additional inputs to a gate merely required additional emitters on a shared base region of

448-494: A new standard. In March 1994, the IEEE 1284 specification was released. 1284 included all of these modes, and allowed operation in any of them. The IEEE 1284 standard allows for faster throughput and bidirectional data flow with a theoretical maximum throughput of 4 MB/s; actual throughput is around 2 MB/s depending on hardware. In the printer venue, this allows for faster printing and back-channel status and management. Since

504-510: A parallel port can operate the port in ECP or EPP mode, or both simultaneously. IEEE-1284 requires that bi-directional device communication is always initiated in Nibble Mode. If the host receives no reply in this mode, it will assume that the device is a legacy printer, and enter Compatibility Mode. Otherwise, the best mode that is supported on both sides of the connection is negotiated between

560-430: A richer set of status codes were desired. This led to an early expansion of the system introduced by HP , the "Bitronics" implementation released in 1992. This used the status pins of the original port to form a 4-bit parallel port for sending arbitrary data back to the host. A further modification, "Bi-Directional", used the status pins to indicate the direction of data flow on the 8-bit main data bus; by indicating there

616-415: A series of solenoids to pull the individual metal pins to strike a ribbon and the paper. A dot matrix print head consists of a series of metal pins arranged in a vertical row. Each pin is attached to some sort of actuator, a solenoid in the case of Centronics, which can pull the pin forward to strike a ribbon and the paper. The entire print head is moved horizontally in order to print a line of text, striking

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672-420: A standard TTL input while not allowing the voltage to rise to more than 0.4 volts. The output stage of the most common TTL gates is specified to function correctly when driving up to 10 standard input stages (a fanout of 10). TTL inputs are sometimes simply left floating to provide a logical "1", though this usage is not recommended. Standard TTL circuits operate with a 5- volt power supply. A TTL input signal

728-537: A time (as in Morse code and BPSK ), well-known techniques such as PSM , PAM , and Multiple-input multiple-output communication send a few bits in parallel. (Each such group of bits is called a " symbol "). Such techniques can be extended to send an entire byte at once ( 256-QAM ). Transistor%E2%80%93transistor logic Transistor–transistor logic ( TTL ) is a logic family built from bipolar junction transistors . Its name signifies that transistors perform both

784-697: A wide range of logic gates , flip-flops , counters, and other circuits. Variations of the original TTL circuit design offered higher speed or lower power dissipation to allow design optimization. TTL devices were originally made in ceramic and plastic dual in-line package (s) and in flat-pack form. Some TTL chips are now also made in surface-mount technology packages. TTL became the foundation of computers and other digital electronics. Even after Very-Large-Scale Integration (VLSI) CMOS integrated circuit microprocessors made multiple-chip processors obsolete, TTL devices still found extensive use as glue logic interfacing between more densely integrated components. TTL

840-501: Is a common debug interface for embedded devices. Handheld devices such as graphing calculators and NMEA 0183 -compliant GPS receivers and fishfinders also commonly use UART with TTL. TTL serial is only a de facto standard: there are no strict electrical guidelines. Driver–receiver modules interface between TTL and longer-range serial standards: one example is the MAX232 , which converts from and to RS-232 . Differential TTL

896-428: Is and always has been widely used within integrated circuits , in peripheral buses, and in memory devices such as RAM . Computer system buses, on the other hand, have evolved over time: parallel communication was commonly used in earlier system buses, whereas serial communications are prevalent in modern computers. Before the development of high-speed serial technologies, the choice of parallel links over serial links

952-504: Is applied to many successive generations of bipolar logic, with gradual improvements in speed and power consumption over about two decades. The most recently introduced family 74Fxx is still sold today (as of 2019), and was widely used into the late 90s. 74AS/ALS Advanced Schottky was introduced in 1985. As of 2008, Texas Instruments continues to supply the more general-purpose chips in numerous obsolete technology families, albeit at increased prices. Typically, TTL chips integrate no more than

1008-406: Is buffered by a common emitter amplifier. Inputs both logical ones. When all the inputs are held at high voltage, the base–emitter junctions of the multiple-emitter transistor are reverse-biased. Unlike DTL, a small “collector” current (approximately 10 μA) is drawn by each of the inputs. This is because the transistor is in reverse-active mode . An approximately constant current flows from

1064-515: Is defined as "low" when between 0 V and 0.8 V with respect to the ground terminal, and "high" when between 2 V and V CC (5 V), and if a voltage signal ranging between 0.8 V and 2.0 V is sent into the input of a TTL gate, there is no certain response from the gate and therefore it is considered "uncertain" (precise logic levels vary slightly between sub-types and by temperature). TTL outputs are typically restricted to narrower limits of between 0.0 V and 0.4 V for

1120-481: Is substantially slower. Designers can combine ECL and TTL devices in the same system to achieve best overall performance and economy, but level-shifting devices are required between the two logic families. TTL is less sensitive to damage from electrostatic discharge than early CMOS devices. Due to the output structure of TTL devices, the output impedance is asymmetrical between the high and low state, making them unsuitable for driving transmission lines. This drawback

1176-400: Is usually overcome by buffering the outputs with special line-driver devices where signals need to be sent through cables. ECL, by virtue of its symmetric low-impedance output structure, does not have this drawback. The TTL "totem-pole" output structure often has a momentary overlap when both the upper and lower transistors are conducting, resulting in a substantial pulse of current drawn from

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1232-514: The DEC VAX and Data General Eclipse ; however some computer families were based on proprietary components (e.g. Fairchild CTL) while supercomputers and high-end mainframes used emitter-coupled logic . They were also used for equipment such as machine tool numerical controls, printers and video display terminals, and as microprocessors became more functional for "glue logic" applications, such as address decoders and bus drivers, which tie together

1288-438: The "totem-pole" output stage is the decreased voltage level (no more than 3.5 V) of the output logical "1" (even if the output is unloaded). The reasons for this reduction are the voltage drops across the V 3 base–emitter and V 5 anode–cathode junctions. Like DTL, TTL is a current-sinking logic since a current must be drawn from inputs to bring them to a logic 0 voltage level. The driving stage must absorb up to 1.6 mA from

1344-406: The 1990s. Until the advent of programmable logic , discrete bipolar logic was used to prototype and emulate microarchitectures under development. TTL inputs are the emitters of bipolar transistors. In the case of NAND inputs, the inputs are the emitters of multiple-emitter transistors , functionally equivalent to multiple transistors where the bases and collectors are tied together. The output

1400-404: The 7401 and 7403 series. Open-collector outputs of some gates have a higher maximum voltage, such as 15 V for the 7426, useful when driving non-TTL loads. To solve the problem with the high output resistance of the simple output stage the second schematic adds to this a "totem-pole" (" push–pull ") output. It consists of the two n-p-n transistors V 3 and V 4 , the "lifting" diode V 5 and

1456-541: The Eastern Bloc (Soviet Union, GDR, Poland, Czechoslovakia, Hungary, Romania — for details see 7400 series ). Not only did others make compatible TTL parts, but compatible parts were made using many other circuit technologies as well. At least one manufacturer, IBM , produced non-compatible TTL circuits for its own use; IBM used the technology in the IBM System/38 , IBM 4300 , and IBM 3081 . The term "TTL"

1512-452: The bottom of the resistor and ground. If one input voltage becomes zero, the corresponding base–emitter junction of the multiple-emitter transistor is in parallel with these two junctions. A phenomenon called current steering means that when two voltage-stable elements with different threshold voltages are connected in parallel, the current flows through the path with the smaller threshold voltage. That is, current flows out of this input and into

1568-628: The controls of the Phoenix missile . TTL became popular with electronic systems designers after Texas Instruments introduced the 5400 series of ICs, with military temperature range, in 1964 and the later 7400 series , specified over a narrower range and with inexpensive plastic packages, in 1966. The Texas Instruments 7400 family became an industry standard. Compatible parts were made by Motorola , AMD , Fairchild , Intel , Intersil , Signetics , Mullard , Siemens , SGS-Thomson , Rifa , National Semiconductor , and many other companies, even in

1624-407: The cost of memory dropped, printers began adding increasing amounts of buffer memory, initially a line or two, but then whole pages and then documents. The original port design was send-only, allowing data to be sent from the host computer to the printer. Separate pins in the port allow status information to be sent back to the computer. This was a serious limitation as printers became "smarter" and

1680-424: The current-limiting resistor R 3 (see the figure on the right). It is driven by applying the same current steering idea as above. When V 2 is "off", V 4 is "off" as well and V 3 operates in active region as a voltage follower producing high output voltage (logical "1"). When V 2 is "on", it activates V 4 , driving low voltage (logical "0") to the output. Again there is a current-steering effect:

1736-436: The digital domain but would not ordinarily be used where analog amplification is the primary purpose. TTL inverters can also be used in crystal oscillators where their analog amplification ability is significant. A TTL gate may operate inadvertently as an analog amplifier if the input is connected to a slowly changing input signal that traverses the unspecified region from 0.8 V to 2 V. The output can be erratic when

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1792-784: The diode. However, this technique actually converts the sophisticated "totem-pole" output into a simple output stage having significant output resistance when driving a high level (determined by the external resistor). Like most integrated circuits of the period 1963–1990, commercial TTL devices are usually packaged in dual in-line packages (DIPs), usually with 14 to 24 pins, for through-hole or socket mounting. Epoxy plastic (PDIP) packages were often used for commercial temperature range components, while ceramic packages (CDIP) were used for military temperature range parts. Beam-lead chip dies without packages were made for assembly into larger arrays as hybrid integrated circuits. Parts for military and aerospace applications were packaged in flatpacks ,

1848-414: The equivalent TTL component and with the same pinouts . For example, the 74HCT00 series provides many drop-in replacements for bipolar 7400 series parts, but uses CMOS technology. Successive generations of technology produced compatible parts with improved power consumption or switching speed, or both. Although vendors uniformly marketed these various product lines as TTL with Schottky diodes , some of

1904-501: The function blocks realized in VLSI elements. The Gigatron TTL is a more recent (2018) example of a processor built entirely with TTL integrated circuits. While originally designed to handle logic-level digital signals, a TTL inverter can be biased as an analog amplifier. Connecting a resistor between the output and the input biases the TTL element as a negative feedback amplifier . Such amplifiers may be useful to convert analog signals to

1960-463: The host and client devices by exchanging standardized Nibble Mode messages. An IEEE-compliant cable must meet several standards of wiring and quality. Three types of connectors are defined: There are two kinds of IEEE 1284 cables: In IEEE 1284 Daisy Chain Specification, up to eight devices can be connected to a single parallel port. All modes use TTL voltage logic levels , which limits

2016-505: The input is in this range. A slowly changing input like this can also cause excess power dissipation in the output circuit. If such an analog input must be used, there are specialized TTL parts with Schmitt trigger inputs available that will reliably convert the analog input to a digital value, effectively operating as a one bit A to D converter. TTL serial refers to single-ended serial communication using raw transistor voltage levels: "low" for 0 and "high" for 1. UART over TTL serial

2072-685: The input transistor. If individually packaged transistors were used, the cost of all the transistors would discourage one from using such an input structure. But in an integrated circuit, the additional emitters for extra gate inputs add only a small area. At least one computer manufacturer, IBM, built its own flip chip integrated circuits with TTL; these chips were mounted on ceramic multi-chip modules. TTL devices consume substantially more power than equivalent CMOS devices at rest, but power consumption does not increase with clock speed as rapidly as for CMOS devices. Compared to contemporary ECL circuits, TTL uses less power and has easier design rules but

2128-648: The logic function (the first "transistor") and the amplifying function (the second "transistor"), as opposed to earlier resistor–transistor logic (RTL) and diode–transistor logic (DTL). TTL integrated circuits (ICs) were widely used in applications such as computers , industrial controls, test equipment and instrumentation, consumer electronics, and synthesizers . After their introduction in integrated circuit form in 1963 by Sylvania Electric Products , TTL integrated circuits were manufactured by several semiconductor companies. The 7400 series by Texas Instruments became particularly popular. TTL manufacturers offered

2184-513: The military-specification temperature range of −55 to +125 °C. Special quality levels and high-reliability parts are available for military and aerospace applications. Radiation-hardened devices (for example from the SNJ54 series) are offered for space applications. Before the advent of VLSI devices, TTL integrated circuits were a standard method of construction for the processors of minicomputer and midrange mainframe computers, such as

2240-641: The new standard allowed the peripheral to send large amounts of data back to the host, devices that had previously used SCSI interfaces could be produced at a much lower cost. This included scanners , tape drives , hard disks , computer networks connected directly via parallel interface, network adapters and other devices. No longer was the consumer required to purchase an expensive SCSI card—they could simply use their built-in parallel interface. The parallel interface has since been mostly displaced by local area network interfaces and USB 2.0 . IEEE 1284 can operate in five modes: Most recent computers that include

2296-464: The output is needed to drive an input into an undefined region. In some cases (e.g., when the output of a TTL logic gate needs to be used for driving the input of a CMOS gate), the voltage level of the "totem-pole" output stage at output logical "1" can be increased closer to V CC by connecting an external resistor between the V4 collector and the positive rail. It pulls up the V 5 cathode and cuts-off

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2352-449: The output is not loaded. A common variation omits the collector resistor of the output transistor, making an open-collector output. This allows the designer to fabricate wired logic by connecting the open-collector outputs of several logic gates together and providing a single external pull-up resistor . If any of the logic gates becomes logic low (transistor conducting), the combined output will be low. Examples of this type of gate are

2408-423: The output stage. The main advantage of TTL with a "totem-pole" output stage is the low output resistance at output logical "1". It is determined by the upper output transistor V 3 operating in active region as an emitter follower . The resistor R 3 does not increase the output resistance since it is connected in the V 3 collector and its influence is compensated by the negative feedback. A disadvantage of

2464-425: The paper several times to produce a matrix for each character. Character sets on early printers normally used 7 by 5 "pixels" to produce 80-column text. The complexity of printing a character as a sequence of columns of dots is managed by the printer electronics, which receives character encodings from the computer one at a time, with the bits transferred serially or in parallel. As printers grew in sophistication, and

2520-425: The positive rail, through the resistor and into the base of the multiple emitter transistor. This current passes through the base–emitter junction of the output transistor, allowing it to conduct and pulling the output voltage low (logical zero). An input logical zero. Note that the base–collector junction of the multiple-emitter transistor and the base–emitter junction of the output transistor are in series between

2576-487: The possible cable length to a few meters unless expensive special cables are used. The following are the typical colors found on 25-pin IEEE 1284 cable leads. Parallel communications The basic difference between a parallel and a serial communication channel is the number of electrical conductors used at the physical layer to convey bits. Parallel communication implies more than one such conductor. For example, an 8-bit parallel channel will convey eight bits (or

2632-510: The power supply. These pulses can couple in unexpected ways between multiple integrated circuit packages, resulting in reduced noise margin and lower performance. TTL systems usually have a decoupling capacitor for every one or two IC packages, so that a current pulse from one TTL chip does not momentarily reduce the supply voltage to another. Since the mid 1980s, several manufacturers supply CMOS logic equivalents with TTL-compatible input and output levels, usually bearing part numbers similar to

2688-417: The resistor R 3 limits the current flowing directly through the series connected transistor V 3 , diode V 5 and transistor V 4 that are all conducting. It also limits the output current in the case of output logical "1" and short connection to the ground. The strength of the gate may be increased without proportionally affecting the power consumption by removing the pull-up and pull-down resistors from

2744-405: The series combination of V 2 's C-E junction and V 4 's B-E junction is in parallel with the series of V 3 B-E, V 5 's anode-cathode junction, and V 4 C-E. The second series combination has the higher threshold voltage, so no current flows through it, i.e. V 3 base current is deprived. Transistor V 3 turns "off" and it does not impact on the output. In the middle of the transition,

2800-414: The transition over a diode input structure. The main disadvantage of TTL with a simple output stage is the relatively high output resistance at output logical "1" that is completely determined by the output collector resistor. It limits the number of inputs that can be connected (the fanout ). Some advantage of the simple output stage is the high voltage level (up to V CC ) of the output logical "1" when

2856-559: The underlying circuits, such as used in the LS family, could rather be considered DTL . Variations of and successors to the basic TTL family, which has a typical gate propagation delay of 10ns and a power dissipation of 10 mW per gate, for a power–delay product (PDP) or switching energy of about 100 pJ , include: Most manufacturers offer commercial and extended temperature ranges: for example Texas Instruments 7400 series parts are rated from 0 to 70 °C, and 5400 series devices over

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2912-430: The zero (low) voltage source. As a result, no current flows through the base of the output transistor, causing it to stop conducting and the output voltage becomes high (logical one). During the transition the input transistor is briefly in its active region; so it draws a large current away from the base of the output transistor and thus quickly discharges its base. This is a critical advantage of TTL over DTL that speeds up

2968-491: Was data to send to the host on one of the pins, all eight data pins became available for use. This proved adaptable, and led to the "Enhanced Parallel Port" standard, which worked like Bi-Directional mode but greatly increased the signalling speeds to 2  MB /s, and later the "Extended Capability Port" version increased this to 2.5 MB/s. In 1991 the Network Printing Alliance was formed to develop

3024-452: Was driven by these factors: The decreasing cost and better performance of integrated circuits has led to serial links being used in favor of parallel links; for example, IEEE 1284 printer ports vs. USB , Parallel ATA vs. Serial ATA , and FireWire or Thunderbolt are now the most common connectors for transferring data from audiovisual (AV) devices such as digital cameras or professional-grade scanners that used to require purchasing

3080-506: Was invented in 1961 by James L. Buie of TRW , which declared it "particularly suited to the newly developing integrated circuit design technology." The original name for TTL was transistor-coupled transistor logic (TCTL). The first commercial integrated-circuit TTL devices were manufactured by Sylvania in 1963, called the Sylvania Universal High-Level Logic family (SUHL). The Sylvania parts were used in

3136-451: Was not available in 1971. The Datapoint 2200 from 1970 used TTL components for its CPU and was the basis for the 8008 and later the x86 instruction set. The 1973 Xerox Alto and 1981 Star workstations, which introduced the graphical user interface , used TTL circuits integrated at the level of arithmetic logic units (ALUs) and bitslices, respectively. Most computers used TTL-compatible " glue logic " between larger chips well into

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