Logic Familys

[begin-quote]

Logic Family Choices

With about 20 logic families now extant, some comments are in order about which to use for teaching lab excercises and projects. You are aware, I sincerely hope, that Morse Teaching Center policy is to simplify ordering and to lessen confusion among TAs and students by insisting on close adherence to a set of Recommended Parts. To be sure, such a list will never be complete, so we are willing to expand it as your needs evolve, but the process should be governed by informed choice. We don't want our lab activities to become historic restoration projects.

This first figure comes from a Texas Instruments promotional brochure but is a convenient way of showing most (not all) logic families and where they fit generationally. The original TTL family (e.g. 7400, 7493) had its heyday 20 years ago and is thoroughly obsolete. One of its prominent successors, the 74ALSxxx family, is still quite current and readily available.

But with CMOS becoming the hugely dominant force in logic integration, this is what we should expose students to. The best choice for general logic experiments and design is the 74HCxxx family. So the modern 74HC76 will be a supply-voltage (+5V) and pin-compatible dual flip-flop like the old 7476. For those interested in more details, the electrical characteristics of the major families are in Table 9.1 (pictured below) from Horowitz & Hill "The Art of Electronics," with much additional information in the rest of chapt. 9

Not all logic functions you might will be available in the modern HC and HCT families, especially when it comes to specialized interface functions like display drivers. In those cases we need to resort to ALS or even LS. But always please consider if redesign can bring your logic needs into the HC family. When a design has to mix logic families, some care may be indicated as per the interconnection guidelines in Horowitz & Hill Table 9.2. (pictured below)

Lou Berman and I are ready to work with you on clarifying any particulars of logic IC (and other component) choices, to bring them into harmony with, and constructively evolve, our " Recommended Parts" library.

TABLE 9.1. -- LOGIC FAMILIES

t_pd(’00)
(C_L=50pF)

P_diss

V_supply

f_clk(’74)

(C_L=0)

I_OL

I_IL

V_th

Date

Family

typ
(ns)

max
(ns)

max
(MHz)

@1MHz
(mW/gate)

@0.5V max
(mA)

max
(mA)

typ
(V)

min
(V)

nom
(V)

max
(V)

of intro

CMOS

AC
ACT

5.1

125

0.5

V₊/2
1.4

2
4.5

5 or 3.3
5

6
5.5

1985

HC
HCT

0.5

V₊/2
1.4

2
4.5

5
5

6
5.5

1982

4000B/74C

@10V
@5V

30
50

60
90

5
2

1.2
0.3

1.3
0.5

0
0

V₊/2

5-15

1970

TTL

4.5

105

0.5

1.5

4.5

5.5

1980

3.5

100

5.4

0.6

1.6

4.75

5.25

1979

ALS

1.3

0.1

1.4

4.5

5.5

1980

0.4

1.1

4.75

5.25

1976

TABLE 9.2. -- LOGIC FAMILIES CONNECTIONS

TO *FROM*	TTL	HCT ACT	HC AC	HC, AC @3.3V	NMOS LSI	4000B, 74C @5V	4000B, 74C @10V
TTL	OK	OK	A	OK	OK	A	B
HCT ACT	OK	OK	OK	NO	OK	OK	B
HC AC	OK	OK	OK	NO	OK	OK	B
HC, AC @3.3V	OK	OK	NO	OK	OK	B	B
NMOS LSI	OK	OK	A	OK	OK	A	B
4000B, 74C @5V	OK^a	OK	OK	NO	OK	OK	B
4000B, 74C @10V	C	C	C	C	C	C	OK

^(a) with limited fanout.

A - pullup to +5V, or use HCT as interface.

B - use i)OC pullup to +10V, or ii)40109, 14504, or LTC1045 level translator.

C - use 74C901/2, 4049/50, 14504, or LTC1045 level translator.

[end-quote -- from http://www.eng.yale.edu/ee-labs/morse/main.htm ]

The Art of Electronics (Horowitz & Hill, Cambridge University Press, ISBN 0-521-37095-7) On page 574 is a nice little table that lists what you can drive with what.

              TTL | HCT/ACT | HC/AC | 4000B/74C@5v |
           +------+---------+-------+--------------+
 TTL       |  OK  |   OK    |   A   |       A      |
           +------+---------+-------+--------------+
 HCT/ACT   |  OK  |   OK    |   OK  |       OK     |
           +------+---------+-------+--------------+
 HC/AC     |  OK  |   OK    |   OK  |       OK     |
           +------+---------+-------+--------------+
 4000B/74C | OK * |   OK    |   OK  |       OK     |
  @5v      |      |         |       |              |
           +------+---------+-------+--------------+

See:

Questions:

dalem@isco.com asks:
We are using HCT and AHCT parts in a processor buss design. We are seeing various degrees of ringing and overshoot. What is an exceptable amount of this type of effect? It does not seem to be a problem, but how can one reduce the ringing and overshoot.

The only real problems caused by ringing and overshoot are EMI and false or repeated triggering in extreme cases. And higher power consumption to some degree... To reduce:
A) Use a slower, lower power logic family.
B) put a low value resistor in SERIES (not parallel) with each signal. You will see the ringing and overshoot decrease as the resistance is increased. This will also cause the signal transitions to be slower and may (not very likely) make small changes to timing as the resistance becomes too much.
This will also decrease noise in the system and drop power use a little.

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Logic Familys

A - Advanced

L - Low

S - Schottky

C - CMOS interface (not necessarily CMOS components but designed for connection to other CMOS devices)

T - TTL interface (not necessarily TTL components but designed for connection to other TTL devices) Devices are assumed to be TTL unless otherwise specified.

F - Fast TTL.

(none) 74xxx TTL Fast, high power, lots of supply noise
(none) 4xxx CMOS slow, low power, low supply noise
L - Low-Power TTL
- LS Low-Power Schottky Logic low speed, low drive, 5 V VCC
- LV Low-Voltage CMOS Technology low speed, low drive
  - LVC
  - LVT
H - High speed TTL (High speed for the time, pretty slow compared to newer types)
- HC - High-Speed CMOS Logic low speed, low drive, 5 V VCC For low-power logic requirements. typical propagation delays of 15.6 ns. 80 µA maximum static current. CMOS-compatible inputs
  - HCT - TTL-compatible inputs.
A - Advanced
- AC - Advanced CMOS. Medium speed, medium drive (24 mA), 5 V VCC
  - ACT - TTL-compatible inputs.
- AHC - Advanced High-Speed CMOS Logic medium speed, low drive, 5 V VCC. For HCMOS users who need more speed for low-power, low-noise, and low-drive applications. typical propagation delays of 5.2 ns (octals), which is about three times faster than HC devices. 40 µA maximum static current, half that of HCMOS. Output-drive current is ±8 mA at 5 V VCC and ±4 mA at 3.3 V VCC. CMOS-compatible inputs
  - AHCT - TTL-compatible inputs.
- AS - Advanced Schottky Logic. medium speed, high drive, 5 V VCC
- ALS - Advanced Low-Power Schottky Logic low speed, high drive, 5 V VCC
F - Fast Schottky. Logic medium speed, high drive, 5 V VCC 74F logic is a general-purpose family of high-speed advanced bipolar logic.