7400 series of TTL

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7400 series of TTL

Written by goldeneggs

Wednesday, 05 November 2008 07:49

The 7400 series of TTL integrated circuits are historically important as the first widespread family of IC logic. It was used to build the mini and mainframe computers of the sixties and seventies. Several generations of pin-compatible descendants of the original family has since been de-facto standard-components for more than 40 years, and seen use in many types of products and equipment besides computers.

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 indicates 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, cheap surface-mounted CMOS versions of the 7400 series are used in consumer electronics and for glue logic in computers and industrial electronics, along with modern variants of the equally important 4000 series. The fastest parts are surface-mount only, but hole-mounted devices, which are very useful for rapid breadboard-prototyping and education, are also readily available.
The 14-pin DIP shown to the right 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, the two additional contacts supply power (+5 V) and connect the ground. (The former Soviet Union manufactured the K155ЛA3 which was pin-compatible with the 7400 part available in the United States.[2])
While designed as a family of digital logic, it was not unusual to see TTL-chips in analog circuits like Schmitt triggers, various generators or voltage stabilizers.[citation needed] Like the 4000 series, the newer CMOS versions of the 7400 series are also perfectly usable as analog (often audio) amplifiers using negative feedback (similar to operational amplifiers with only an inverting input).
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7400 series subfamilies

Early 7400 series parts were constructed using bipolar transistors. Newer sub-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 4000 series of CMOS devices. Bipolar devices are also limited to a fixed power supply voltage, typically 5V, while CMOS parts often support a range of supply voltages.
Milspec rated devices for use in extended temperature conditions are available as the 5400 series. A shortlived 6400 series was rated for an intermediate (industrial) temperature range.
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. Strictly, an integrated circuit made in CMOS is no longer a TTL chip since it uses FETs and not bipolar junction transistors, but similar part numbers are retained to identify similar logic functions in the different subfamilies.

Bipolar
- L - Low power, very slow (rendered obsolete by the LS-series)
- H - High speed (rendered obsolete 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)
CMOS
- C - CMOS 4-15V operation similar to 4000 series
- HC - High speed CMOS, similar performance to LS
- 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
- FC - Fast CMOS, performance similar to F
- LCX - CMOS with 3V supply and 5V tolerant inputs
- LVQ - Low voltage - 3.3V
- LVX - Low voltage - 3.3V with 5V tolerant inputs
- VHC - Very High Speed CMOS - 'S' performance in CMOS technology and power
- G - Super high speeds at more than 1 GHz (Produced by Potato Semiconductor)
BiCMOS
- 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 3.3V cmos signals. The non-T parts have conventional CMOS input thresholds.
The 74L family is a relatively low-power, but slower version of the 74 family.
The 74H family is the same basic design as the 7400 family with resistor values reduced. This reduced the typical propagation delay from 9ns to 6ns but increased the power consumption. The 74H family provided a number of unique devices for CPU designs in the 1970s.
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 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 microprocessor and personal computer CPU devices.

History

Although the 7400 series was the first de facto industry standard TTL logic family, 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, and the Signetics 8200 family.
The 7400 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.
As of 2007, individual chips can be purchased for approximately 0.25 USD each, depending on the particular chip. Purchased in bulk the price per unit falls to even lower prices per package.

Part numbering scheme

The part numbers for 7400 series logic devices often use the following naming convention, though specifics vary between manufacturers.

First a two or three letter prefix which indicates the manufacturer of the device
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.
Two or more digits assigned for each device. There are hundreds of different devices in each family but when this number is the same, the function and pin-out of the chip is nearly always the same regardless of manufacturer -- exceptions include some flat-pack devices, surface-mount devices, some of the faster CMOS series (for example 74AC), and at least one low-power TTL device has a different pin-out than the regular series part.
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 SN74ALS245 means this is a device made by Texas Instruments, it is a commercial temperature range TTL device, it is a member of the "advanced low-power Schottky" family, and it is a bi-directional eight bit buffer.
Many logic families keep the numeric sequence of a similar TTL device as an aid to designers.

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