74xx

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Some 74xx chips in the DIL housing .
Terminal assignment (newer American symbols) and picture of the SN7400, a quadruple NAND gate with two inputs each.
Motherboard of the first IBM PC from 1981. With the exception of the block of 32 RAM memory chips from AMD at the bottom right, almost all ICs of this size are of the 74LS type.

A group of integrated circuits (ICs) in digital electronics is called 74xx chips . The numbers of all these circuits (chips) begin with the digits "74", hence the name. The simplest, first developed electronic chips of the series contain simple logical basic functions in the form of logic gates (AND, OR etc.), which were initially implemented as transistor-transistor logic . In the later development, circuit functions up to complex arithmetic units were integrated in these components .

history

The series was developed by Texas Instruments in the 1970s and is still being expanded. The oldest chips have existed practically unchanged since then. The sequence of digits with four to six digits is incremented continuously. The best-known representative is the 7400, a 4-way NAND gate with two inputs each.

In the meantime, various 74xx logic families have been developed that have been improved compared to the original, especially in terms of speed and power consumption. They are identified by additional letters (one or up to five letters) between "74" and "xx", for example 74LS00 (Low Power Schottky or Schottky-TTL ). The original series (without additional letters) has lost much of its importance today and is rarely used. The early home and personal computers of the 1970s and 1980s usually contained a large number of these chips. They were later largely replaced in computer technology by customer-specific, complex ICs ( ASICs ), each of which can replace a large number of 74xx ICs.

casing

Most of the 74xx chips exist as DIL housings and as SMD modules in SMD housing forms . They are offered by many semiconductor manufacturers with different prefixed code letters . Logic components are also available in a ceramic DIL housing.

Operating voltage

The original logic families were operated with a supply voltage of 5.0 V. As a further development of logic families in the direction of ever higher frequencies, the operating voltage was also reduced to 3.3 V or 2.5 V, for example. To connect logic families with different operating voltages (e.g. 3.3 V to 5.0 V), special logic families have been developed that have logic levels at the input and output that are compatible with other logic families.

Logic families

The original logic families were made in bipolar technology. In the course of time, logic families in CMOS technology and BiCMOS technology have been added. The logic families for very high clock frequencies are now almost exclusively implemented in CMOS or BiCMOS technology.

Abbreviations and brief descriptions of variants from the TTL family
abbreviation designation description
Bipolar
- Standard TTL -
L. Low power Further development with lower power requirements; very slowly; obsolete and replaced by the LS series
H High speed Further development with higher switching speed; obsolete and replaced by the S series; often used in computers in the 1970s
S. Schottky outdated
LS Low power Schottky
AS Advanced Schottky
AS Advanced Low Power Schottky
F. Nearly Faster than the S series; comparable to the AS series
CMOS
C. CMOS Supply voltage from 5 to 15 V, similar to the 4000 logic family
HC High speed CMOS Supply voltage from 2 to 6 V, similar speed to LS 12 ns,
HCU High speed CMOS unbuffered Similar to HC, only without a buffer stage at the input and output
HCT High speed Logic level compatible with TTL, only suitable for 5 volts
AC Advanced CMOS  
ACT Advanced CMOS Logic level compatible with TTL 
AHC Advanced high-speed CMOS HC series with approx. 3 times the speed
AHCT Advanced high-speed CMOS fast HC series with TTL-compatible logic levels
ALVC Low voltage Low supply voltage of 1.65 to 3.6 V, running time 2 ns
AUC Low voltage Low supply voltage of 0.8 to 2.7 V, running time less than 1.9 ns at 1.8 V.
FC Almost CMOS Comparable to F
LCX Supply voltage 3.3 V; 5 V tolerant inputs
LVC Low voltage Supply voltage 1.65 to 5.5 V; 5 V tolerant inputs even with supply voltages <5 V.
LVQ Low voltage Supply voltage 3.3 V.
LVX Low voltage Supply voltage 3.3 V; 5 V tolerant inputs
VHC Very high speed CMOS Similar to 'S' but in CMOS
CBT Very fast CMOS family for applications up to the GHz range; Supply voltage 5.0 V.
CBTLV Low voltage Very fast CMOS family for applications up to the GHz range, supply voltage 3.3 V.
G Super high speeds For switching frequencies up to 1 GHz, supply voltage 1.65 to 3.3 V; 5 V tolerant inputs
BiCMOS
BCT BiCMOS Logic level compatible with TTL, primarily used for buffers.
ABT Advanced BiCMOS TTL compatible logic level, faster than ACT and BCT
ALB Advanced BiCMOS fast BiCMOS technology, supply voltage 3.3 V; used primarily for buffers
ALVT Advanced BiCMOS low voltage fast BiCMOS technology, supply voltage 3.3 V; also 5 V tolerant; used primarily for buffers
LVT Advanced BiCMOS low voltage fast BiCMOS technology, supply voltage 3.3 V; also 5 V tolerant; primarily for buffers

Circuit development

In circuit development, logic families dominate today with low power consumption and a high maximum switching frequency. In practice, logic families with 3.3 V or 2.5 V are often used, since other components, for example PLDs , FPGAs , ASICs and modern microprocessors, are now also operated with the lower supply voltages . Furthermore, individual gate functions or individual flip-flops are practically no longer of any significance in the development of new assemblies. As far as possible, more complex logic components are used for this purpose which contain complete circuit functions in one component, or programmable logic components (PLD or FPGA components) are used. The logic components are usually used today in the SMD housing. Semiconductor manufacturers have often developed different component series for use in different continuous operating temperature ranges .

See also

literature

  • The Engineering Staff: The TTL Data Book . tape 1 . Texas Instruments, 1989, ISBN 3-88078-078-1 .
  • User Guide . Philips / NXP , 1997 ( nxp.com [PDF]).
  • without author: digital design seminar . Texas Instruments, 2000.

Web links

Commons : 74xx  - Collection of images, videos, and audio files