The 7400 series of transistor-transistor logic (TTL) integrated circuits are historically important as the first widespread family of TTL integrated circuit logic. It was used to build the mini and mainframe computers of the 1960s and 1970s. Several generations of pin-compatible descendants of the original family have since become de-facto standard electronic components.
The 7400 chip, containing four NANDs
. The second line of smaller numbers (7645) is a date code; this chip was manufactured in the 45th week of 1976. The N suffix on the part number is a vendor-specific code indicating PDIP packaging.
The 7400 series contains hundreds of devices that provide everything from basic logic gates, flip-flops, and counters, to special purpose bus transceivers and Arithmetic Logic Units (ALU). Specific functions are described in a list of 7400 series integrated circuits.
Today, surface-mounted CMOS versions of the 7400 series are used in various applications in electronics and for glue logic in computers and industrial electronics. The original through-hole devices in dual in-line packages (DIP/DIL), which were the mainstay of the industry for many decades, are very useful for rapid breadboard-prototyping and education and so remain available from most manufacturers. The fastest types and very low voltage versions are typically surface-mount only, however.
The 14-pin DIP is an example of a 7400 part. The chip contains four two-input NAND gates. Each gate uses two pins for input and one pin for its output, and the remaining two contacts supply power (+5 V) and connect the ground.
While designed as a family of digital logic, it was not unusual to see TTL chips in analog circuits like Schmitt triggers. Like the 4000 series, the newer CMOS versions of the 7400 series are also usable as analog amplifiers using negative feedback (similar to operational amplifiers with only an inverting input).
The former Soviet Union manufactured the K155 A3 which was pin-compatible with the 7400 part available in the United States, except for using a metric spacing of 2.5mm between pins instead of the 1/10"-based (2.54mm) spacing used in the west.
7400 series derivative families
7400 series parts were constructed using bipolar transistors, forming what is referred to as transistor transistor logic or TTL. Newer series, more or less compatible in function and logic level with the original parts, use CMOS technology or a combination of the two (BiCMOS). Originally the bipolar circuits provided higher speed but consumed more power than the competing 4000 series of CMOS devices. Bipolar devices are also limited to a fixed power supply voltage, typically 5 V, while CMOS parts often support a range of supply voltages.
Part of the 7400 series: Cascadable 8-bit ALU Texas Instruments SN74AS888
Milspec-rated devices for use in extended temperature conditions are available as the 5400 series. Texas Instruments also manufactured radiation-hardened devices with the prefix RSN, and the company offered beam-lead bare dies for integration into hybrid circuits with a BL prefix designation. 
Regular speed TTL parts were also available for a time in the 6400 series - these had an extended industrial temperature range of 40 C to +85 C. While companies such as Mullard listed 6400-series compatible parts in 1970 data sheets, by 1973 there was no mention of the 6400 family in the Texas Instruments TTL Data Book. Some companies have also offered industrial extended temperature range variants using the regular 7400 series part numbers with a prefix or suffix to indicate the temperature grade.
As integrated circuits in the 7400 series were made in different technologies, usually compatibility was retained with the original TTL logic levels and power supply voltages. An integrated circuit made in CMOS is not a TTL chip since it uses field-effect transistors (FETs) and not bipolar junction transistors, but similar part numbers are retained to identify similar logic functions and electrical (power and I/O voltage) compatibility in the different subfamilies. Over 40 different logic subfamilies use this standardized part number scheme.
- 74 - the "standard TTL" logic family had no letters between the "74" and the specific part number.
- 74L - Low power (compared to the original TTL logic family), very slow
- H - High speed (still produced but generally superseded by the S-series, used in 1970s era computers)
- S - Schottky (obsolete)
- LS - Low Power Schottky
- AS - Advanced Schottky
- ALS - Advanced Low Power Schottky
- F - Fast (faster than normal Schottky, similar to AS)
- C - CMOS 4 15 V operation similar to buffered 4000 (4000B) series
- HC - High speed CMOS, similar performance to LS, 12 nS
- HCT - High speed, compatible logic levels to bipolar parts
- AC - Advanced CMOS, performance generally between S and F
- AHC - Advanced High-Speed CMOS, three times as fast as HC
- ALVC - Low voltage - 1.65 to 3.3 V, Time Propagation Delay (TPD) 2 nS
- AUC - Low voltage - 0.8 to 2.7 V, TPD 
- FC - Fast CMOS, performance similar to F
- LCX - CMOS with 3 V supply and 5 V tolerant inputs
- LVC - Low voltage 1.65 to 3.3 V and 5 V tolerant inputs, tpd 
- LVQ - Low voltage - 3.3 V
- LVX - Low voltage - 3.3 V with 5 V tolerant inputs
- VHC - Very High Speed CMOS - 'S' performance in CMOS technology and power
- BCT - BiCMOS, TTL-compatible input thresholds, used for buffers
- ABT - Advanced BiCMOS, TTL-compatible input thresholds, faster than ACT and BCT
Many parts in the CMOS HC, AC, and FC families are also offered in "T" versions (HCT, ACT, and FCT) which have input thresholds that are compatible with both TTL and 3.3 V CMOS signals. The non-T parts have conventional CMOS input thresholds. The ACTQ family introduced by Fairchild utilizes Quiet Series technology to guarantee quiet output switching and improved dynamic threshold performance. FACT Quiet Series features GTO output control and undershoot corrector in addition to a split ground bus for superior performance. The 74H family is the same basic design as the 7400 family with resistor values reduced. This reduced the typical propagation delay from 9 ns to 6 ns but increased the power consumption. The 74H family provided a number of unique devices for CPU designs in the 1970s. Many designers of military and aerospace equipment used this family over a long period and as they need exact replacements, this family is still produced by Lansdale Semiconductor.
The 74S family, using Schottky circuitry, uses more power than the 74, but is faster. The 74LS family of ICs is a lower-power version of the 74S family, with slightly higher speed but lower power dissipation than the original 74 family; it became the most popular variant once it was widely available.
The 74F family was introduced by Fairchild Semiconductor and adopted by other manufacturers; it is faster than the 74, 74LS and 74S families.
Through the late 1980s and 1990s newer versions of this family were introduced to support the lower operating voltages used in newer CPU devices.
Although the 7400 series was the first de facto industry standard TTL logic family to be second-sourced by several semiconductor companies, there were earlier TTL logic families such as the Sylvania SUHL family, Motorola MC4000 MTTL family (not to be confused with RCA CD4000 CMOS), the National Semiconductor DM8000 family, Fairchild 9300 series, and the Signetics 8200 family.
A 4-bit, 2 register, six assembly language instruction computer made entirely of 74-series chips.
The 7400N quad NAND gate was the first product in the series.
The 5400 and 7400 series were used in many popular minicomputers in the seventies and early eighties. The DEC PDP series 'minis' used the 74181 ALU as the main computing element in the CPU. Other examples were the Data General Nova series and Hewlett-Packard 21MX, 1000, and 3000 series.
Hobbyists and students equipped with wire wrap tools, a 'breadboard' and a 5-volt power supply could also experiment with digital logic referring to how-to articles in Byte magazine and Popular Electronics which featured circuit examples in nearly every issue. In the early days of large-scale IC development, a prototype of a new large-scale integrated circuit might have been developed using TTL chips on several circuit boards, before committing to manufacture of the target device in IC form. This allowed simulation of the finished product and testing of the logic before the availability of software simulations of integrated circuits.
In 1965, typical quantity-one pricing for the SN5400 (military grade, in ceramic welded flat-pack) was around 22 USD. As of 2007, individual commercial-grade chips in molded epoxy (plastic) packages can be purchased for approximately 0.25 USD each, depending on the particular chip. Purchased in bulk the price per unit falls even lower.
Part numbering scheme
The part numbers for 7400 series logic devices often use the following naming convention, though specifics vary between manufacturers.
- First, although sometimes omitted, a two or three letter prefix which indicates the manufacturer of the device (e.g. SN for Texas Instruments, DM for National Semiconductor) although these codes are no longer closely associated with a single manufacturer, for example Fairchild Semiconductor manufactures parts with MM and DM prefixes, and none.
- A two-figure secondary prefix, of which the two most common are "74", indicating a commercial temperature range device and "54", indicating an extended (military) temperature range
- Up to four letters describing the logic subfamily, as listed above (e.g. "LS" or "HCT").
- Two or more digits assigned for each device, e.g. 00 for a quad 2-input NAND gate. There are hundreds of different devices in each family. The allocation of device numbers (and, with a few exceptions, the pin-outs) of the original 7400 family was carried across to the later families, and new numbers allocated for new functions, plus some of the competing CD4000 numbers and pin-outs were included over time. There is no pattern to the allocation of these numbers. The function and pin-out of the chip is nearly always the same for the same device number regardless of subfamily manufacturer exceptions are discussed below.
- Additional suffix letters and numbers may be attached to indicate the package type, quality grade, or other information, but this varies widely by manufacturer.
For example SN74ALS245N means this is a device probably made by Texas Instruments (SN), it is a commercial temperature range TTL device (74), it is a member of the "advanced low-power Schottky" family (ALS), and it is a bi-directional eight-bit buffer (245) in a plastic through-hole DIP package (N).
Many logic families maintain a consistent use of the device numbers, as an aid to designers. Often a part from a different 74x00 subfamily could be substituted ("drop-in replacement") in a circuit, with the same function and pin-out yet more appropriate characteristics for an application (perhaps speed or power consumption), which was a large part of the appeal of the 74C00 series over the competing CD4000B series, for example. But there are a few exceptions where incompatibilities (mainly in pin-out) across the subfamilies occurred, such as:
- some flat-pack devices (e.g. 7400W) and surface-mount devices,
- some of the faster CMOS series (for example 74AC)
- a few low-power TTL devices (e.g. 74L86, 74L9 and 74L95) have a different pin-out than the regular (or even 74LS) series part.
- five versions of the 74x54 (4-Wide AND-OR-INVERT gates IC), namely 7454(N), 7454W, 74H54, 74L54W and 74L54N/74LS54, are different from each other in pin-out and/or function!).
Second sources in Europe and the Eastern Block
Some manufacturers such as Mullard and Siemens had pin-compatible TTL parts but with a completely different numbering scheme, however, data sheets identified the 7400-compatible number as an aid to recognition.
At the time the 7400 series was being made, some European manufacturers (that traditionally followed the Pro Electron naming convention) such as Philips/Mullard produced a series of TTL integrated circuits with part names beginning FJ. Some examples of FJ series are:
- FJH101 (=7430) Single 8-input NAND gate,
- FJH131 (=7400) Quadruple 2-input NAND gate,
- FJH181 (=7454N or J) 2+2+2+2 input AND-OR-NOT gate.
The Soviet Union started manufacturing TTL ICs with 7400 series pin-out in late 1960s and early 1970s. Part numbering is different from the Western series:
- the technology modifications were considered different series, and were identified by different numbered prefixes - 155 series is equivalent to plain 74, 131 series is 74H, 158 series is 74L, 531 series is 74S, 555 series is 74LS, and 1530/1531/1533 are 74F/74AS/74ALS respectively. CMOS elements with TTL pin-out are also available, for example 1564 series is equivalent to 74HC.
- the function of the unit is described with a two-letter code followed by a number
- the first letter represents the functional group - logical, triggers, counters, multiplexers, etc.
- the second letter shows the functional subgroup making the distinction between logical NAND and NOR, D- and JK-triggers, decimal and binary counters, etc.
- the number distinguishes variants with different number of inputs, or different number of elements within a die - 1/ 2/ 3 (LA1/LA2/LA3) are 2 four-input / 1 eight-input / 4 two-input NAND elements respectively (equivalent to 7420/7430/7400)
Before July 1974 the two letters from the functional description were inserted after the first digit of the series. Examples: 1 551 and 155 1 (7420), 1 552 and 155 2 (7474) are the same ICs made at different times.
Clones of the plain 7400 series were also made in other Eastern Block countries
Poland and Czechoslovakia used the 7400 numbering scheme with manufacturer prefixes UCY and MH respectively. Examples: UCY7400, and MH7400.
Hungary also used the 7400 numbering scheme but with manufacturer suffix - 7400 is marked as 7400APC.
- Romania used trimmed 7400 numbering with own manufacturing prefix CDB. Example: CDB4123E is 74123.
- East Germany also used trimmed 7400 numbering without manufacturer prefix or suffix. The prefix D (or E) designates digital IC, and not the manufacturer. Example: D174 is 7474. 74LS clones were designated by the prefix D2; e.g. D200 = 74LS00. In later years East German made clones were also available with standard 74* numbers, usually for export.
No information is available for technology modifications (74H, 74LS, etc.) manufactured outside USSR.
- List of 7400 series integrated circuits
- 4000 series
- List of 4000 series integrated circuits
- Logic gate
- Open collector
- Logic family
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