RTL Cookbook Classic Reprint

RTL Cookbook Classic Reprint

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Description: Partial reprint of a classic book that defined the early history of digital integrated circuits and ultimately led to the microprocessor revolution. The rest of the text may be freely downloaded from < http://www.tinaja.com/ebooks/RTLcb.pdf >.

 
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Contents:
RTL Cookbook

by Don Lancaster

SYNERGETICS

SP

PRESS

3860 West First Street, Thatcher, AZ 85552 USA (928) 428-4073 http://www.tinaja.com

Copyright � 2010 by Synergetics Press Thatcher, Arizona 95552

THIRD EDITION FIRST PRINTING--2010

All rights reserved. Reproduction or use, without express permission of editorial or pictorial content, in any manner, is prohibited. No patent liability is assumed with respect to the use of the information contained herein. While every precaution has been taken in the preperation of this book, the publisher assumes no responsibility for errors or omissions. Neither is any liability assumed for damages resulting from the use of the information contained herein. International Standard Book Number: 1-882193-10-3

Created in the United States of America.

Preface

This book will help the electronics experimenter understand and use the low-cost digital integrated circuits now available for practical, everyday electronics projects. The material presented attempts to shatter the myth that digital IC's are too expensive, too complex, or too awesome to use in telligently in simple circuits. In addition, this book shows the technician the why of digital IC's-how they work, how to use them, and how to design with them. It tells how dig ital instruments work and how to design and build your own fully inte grated IC systems. Also, this book should be valuable to the engineer who is tired of wading through a stack of application notes and pre-IC computer books to try to find realistic and reasonable designs for such things as divide-by-n scalers, low-cost decimal counter/readouts, IC monostables, synchronizers, or other circuits. The three chapters on counting flip-flops, divide-by-n counting, and decimal counting provide circuits virtually ready to drop into systems for immediate use. The reasons this book deals entirely with Resistor-Transistor Logic (RTL) are the relatively low prices of this digital-IC line, the ease with which it can be understood, and the ease with which it can be interfaced with conventional transistor circuitry. The book is organized into two parts, with Chapters 1 through 4 cover ing the more basic aspects of RTL, and Chapters 5 through 8 dealing with the more exotic RTL applications. Chapter 1 contains elementary nomen clature, and discusses power-supply considerations, mounting, construction practices, etc. Chapter 2 has to do with logic, decoders, logic functions, and the methods of coupling RTL to the outside world. Chapter 3 is on multi vibrators; it tells how to build square-wave generators, pulse shapers, asta bles, monostables, and bistables. The next chapter concerns biasing RTL

gates into their amplifying region and building such things as crystal oscil lators, operational amplifiers, dc instrument amplifiers, and comparators. This chapter includes "instant-design" charts for speedy amplifier specifica tion. Duty-cycle integration techniques, useful in tachometers and fre quency discriminators, are covered in this chapter, also. Chapter 5 has to do with the JK and Type-D flip-flops, the eight basic JK flip-flop configurations, and some counter techniques. Here, we also look at the input and output restrictions on counting flip-flops, and investi gate the techniques essential for reliable and predictable operation. Chapter

6 is on divide-by-n counting and scaling-how to build reliable, frequency
independent, low-cost dividers, decoders, counters, and steppers for any desired count. Decimal counters are given thorough coverage in Chapter 7. The final chapter is on digital instruments. It shows how to tie together the circuits in the rest of the book to build frequency counters, digital volt meters, electronic stop watches, and other complete digital systems. I wish to extend my thanks to Billy G. Wood and Rudy O. Nonnenmann for their technical and proofing assistance in putting this book together.

DON LANCASTER

Addendum
It is rare for any technical book written in 1968 to still be in de mand-especially a book on integrated circuits. Apparently, we have a classic of sorts on our hands. Your response to this book so far has gener ated the continuing series of Cookbooks-RTL, TTL, Active Filters, TV Typewriter, CMOS, and the related Users Guide to TTL. Much of the information in this book is now out of date. While you can still buy and use RTL, bigger and better logic families are now avail able. (Check into CMOS in particular.) More critically, the problems and thought processes involved when you are working with digital Ie's have matured and changed dramatically. We simply don't worry about the same things anymore. Rather than try to update this text, we've purposely left things as they were. If for no other reason, this leaves us with an untampered historical record of the thought processes and concepts involved with early pre-MSI digital integrated circuit work. Thanks again for your interest and support of this continuing series.
DON LANCASTER

September 1975

Contents

CHAPTER SOME BASICS

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Types of Logic Gates-Two-Input RTL Digital-Logic Gate-Other Logic Blocks-Multiple-Function ICs-Power Levels-Loading: Fan-In and Fan-Out-Packages and Lead Conventions-Mounting Techniques - Tools- Soldering - Power Requirements-Battery Operation-Line "Burned-Out" Integrated Circuits Requirements - Current Operation-"Bad" and

CHAPTER 2 LOGIC AND SWITCHING CIRCUITS

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31

The Two-Input Gate as a Simple Switch-Computer Logic-Ones and Zeros-The NOT Circuit-Two-Input Logic Functions-Multi pIe-Input Logic-Building Logic Functions With RTL-Choosing Logic Definitions-What Good Is Logic?-Decimal-to-Binary En coder-Binary-to-Decimal Decoder-Indicating States: Driving the Outside World With RTL

CHAPTER 3 MULTIVIBRATORS

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49

Two Inverters Back-to-Back-Triggering: the Bistable Multivibrator -Loading-The Reset-Set Flip-Flop-Triggering Restrictions on the RS Flip-Fop--Counting With RS Flip-Flops-The Monostable Multivibrator-Contact Conditioners-The Half Monostable-The Astable Multivibrator-Other Multivibrator-Type Circuits

CHAPTER 4 LINEAR CIRCUITS AND TECHNIQUES ........ ...... ... .........
RTL Gates as Linear Amplifiers-Characteristic Curves-High

83

Power Operation-Class-A Common-Emitter Amplifier Without Feedback-Class-A Common-Emitter Amplifier With Feedback Differential Amplifiers-Restrictions on the Differential Amplifier -Linear Applications for RTL-Some Typical RTL Linear Circuits -Differential-Amplifier Applications - Comparators - Duty-Cycle Integrators

CHAPTER 5 COUNTING FLIP-FLOPS ....... ......... ... .............. 105
. . .

The

JK Flip-Flop-Using JK Flip-Flops-The Type-D Flip-Flop

Using the Type-D Flip-Flop

CHAPTER 6 SCALING AND DIVIDE-BY-N COUNTING ... ...... ............... 133
Counter Qualities-Design Pitfalls-Low-Modulo Counters-High Modulo Counters-Fractional-Modulo Counters

CHAPTER 7 DECIMAL COUNTING .................... .................. 171
Decimal Counter Applications-Some Practical Decimal Counters A 9's Complement Up-Down Counter

CHAPTER 8 DIGITAL INSTRUMENTS AND OTHER RTL ApPLICATIONS
Digital Instruments-Speed-Accuracy Product-Composite Digital Instruments-Some Relatively Complex RTL Applications-Some Simple RTL Applications

203

INDEX ......... ........................................ 234
.

CHAPTER

1

SOIne Basics

A logic gate is any device that obeys certain predetermined rules to turn an output off or on upon some coincidence of signals at its input. A kitchen-sink faucet is a logic gate-it provides an output if either the hot or cold input is provided with an on signal. This is an example of an "OR" gate. A garden hose is an "AND" logic gate, because both the outdoor faucet and the nozzle valve must be provided with an on command in order for the Output to be turned on. A digital logic gate is a logic gate whose inputs and outputs represent only a "yes" or a "no" command. (That is, either there is a voltage or there is not; things are either on or they are off-there is no halfway condition.) While a digital water source would hardly be useful, there are many advan tages to digital logic. Simple elements are called for; they need only re member a "yes" or a "no." And, with enough serial combinations of yes and no outputs, practically any event or number can be represented. The right combinations of digital logic gates, along with some other slightly more complicated logic blocks, make it possible to build anything from an electronic dice game to a television pattern generator.

TYPES OF LOGIC GATES

There are many forms of logic gates. They may be mechanical, hydraulic, chemical, pneumatic, optical, electromechanical, or electronic. The elec tronic logic is by' far the most prevalent, because of the great number of gates in use by the computer industry. Integrated circuits (IC's) were called upon about a decade ago to reduce the size, cost, and power con sumption of electronic computer gates. As a result, there are many different forms of integrated-circuit digital-logic gates available today. Each of these forms is called a logic family, and is usually identified by three letters, such
7

as RTL, DTL, ECL, MOS, TTL, etc. There are many considerations that enter into the choice of logic family for a given application. These factors include cost, speed, complexity, availability, noise immunity, interfacing, and a dozen other more subtle considerations. An integrated-circuit logic family called RTL, short for Resistor Transistor Logic, has characteristics that make it suitable for experimental work and applications ranging from simple projects through digital instruments and complex systems. The advantages of RTL integrated circuits include relatively low price and good availability. Many of these Ie's cost less than $1.25, and since most of them are multifunction devices which include several digital logic gates or other logic blocks in one package, the per-function cost can be even lower. RTL is easy to interface with conventional npn transistor cir cuits, and in many cases it lends itself to replacement of conventional cir cuitry. This is particularly true of the circuits in Chapter 4. Another ad vantage is that RTL is easy to understand. Compared to other logic families, RTL is relatively "slow"; it may be used only at speeds less than 10 million counts per second. It is somewhat noisy, requires considerable supply power, and is limited in drive capa bility. While these limitations are severe to the large-scale computer de signer, they tend to be of negligible importance in simple circuits contain ing only a few Ie's. With RTL, the total price usually is less than the cost of doing the same job transistors.
TWO-INPUT RTL DIGITAL-LOGIC GATE

(and often a poorer one)

with conventional

The work horse of the RTL logic line is the two-input gate. This gate and its logic symbol are shown in Fig. 1-1. (Throughout this book, we will be using a "shorthand" form of logic symbols in which the symbol for a two-input gate is the same anywhere this particular circuit is used.) Fig.

1-1 shows three resistors and two transistors. The transistors are npn and behave exactly like ordinary silicon transistors. This gate is operated, or conditioned, by either applying positive voltage to the inputs or grounding
+3.6VDC

64D1l

M ,
47011 INPUTS

OOUTPUT

470Q

:=t>-OUTT
(6) Corresponding symbol. Fig. 1-1. Two-input RTL gate.

(A) Equivalent schematic.

8

them. The gate responds by providing either a positive or a grounded output. RTL is a saturated logic family. That is, all the internal transistors are either completely off or conducting the maximum possible current (except for the brief interval during which they switch between these two states). Everything is always either on or off. If both inputs to the two-input gate are grounded, neither base receives current, and both transistors remain off. Since both transistors are off, there is no collector current through either transistor, and thus there can be no current through the 640-ohm collector resistor. There can be no voltage drop across this resistor if there is no current through it, and the output terminal is therefore positive. If a positive voltage is applied to input A, transistor Q1 saturates (turns on) and draws the maximum possible current through the 640-ohm collec tor resistor. The entire supply voltage (less a O.2-volt saturation drop) appears across this resistor, and the output terminal is effectively grounded. The same thing would happen if a positive voltage were applied to termi nal B, except that Q2 would saturate and ground the output. If both A and
B are made positive, the output still is grounded. To make the output pos

itive, both inputs must be grounded. To ground the output, either or both inputs must be made positive. The two-input gate is used to perform decision logic based on the ab sence or coincidence of input signals. The output from one two-input gate may drive several others directly. If two two-input gates are combined back-to-back, a circuit called a multivibrator is produced; it can be made to have a memory, generate pulses, or oscillate, depending on just how the gates are connected. Further, this particular type of RTL two-input gate can be biased into its class-A region and used in low-cost crystal oscillators, input amplifiers, operational amplifiers, and comparators. Thus, the two input gate can be made to serve many purposes in the digital-Ie world.

OTHER LOGIC BLOCKS

While the two-input gate is the most versatile and widely used RTL digital logic block, there are other available logic blocks which are nor mally used in combination to produce desired circuit functions with a min imum number of parts. Actually, we could use nothing but two-input gates in any digital circuit, but most circuits would be far more complicated. We now turn to these other RTL logic blocks to see how they function.
Inverters

A

o

ne-input gate (Fig. 1-2) is called an inverter, or a NOT gate. If the

input is made positive, Q1 receives base current, and the output goes to ground. If the input is grounded, the output goes positive. A positive volt age and a grounded condition are opposites in digital logic. We must have
9

one or the other at any logic terminal at any time. These opposites are called complements; the complement of a grounded terminal is a positive terminal, and vice versa. A logic signal is called either a "I" or a "0." A 0 is a complement of a 1. The 0 is not necessarily associated with the grounded-terminal condition; in fact, 0 usually is associated with the positive terminal condition, as will be shown later. An inverter is a useful device for generating the complement of a logic signal, since it automatically produces a 0 if a 1 appears at the input, and a

1 if a 0 appears at the input. An inverter also makes it possible to change
the meaning, or the definition, of a 1. For certain circuits, we may want a

1 to correspond to the grounded input condition, while other circuits may
operate only with a 1 corresponding to the positive input condition.
+3.6VDC

640Q Ql OUTPUT

470Q

A -/- OUTPUT
(6) Corresponding symbol. Fig. 1�2. One.input gate (inverter).

(A) Equivalent schematic.

Inverters may be used back-to-back in pairs to form a latch or a memory. They may be combined with a capacitor to form a simple pulse shaper, time delay, or oscillator. They also may be biased in their c1ass-A region for operation as a low-level amplifier or a crystal oscillator.

Gates With More Than Two Inputs
Sometimes we want a circuit to respond logically
to

a coincidence or

absence of more than two inputs. In these cases, we can use a three-input gate, a four-input gate, or any gate with a gate expander attached to provide the necessary number of inputs. The three-input gate is shown in Fig. 1-3. This circuit has three transistors and four resistors, and its opera tion is just like that of the inverter and the two-input gate. When any input is positive, the corresponding transistor is saturated, and the output is grounded. When all inputs are grounded, the output swings positive. As with the two-input gate and the inverter, the three-input gate inverts the logic, and produces a complementary output. Positive at the input pro vides ground at the output. Adding one more resistor and transistor to the three-input gate makes a four-input gate (Fig. 1-4). Here, the output is grounded if any of the four inputs receives base current, and positive only if all four inputs do
10

+3.6VDC

64011

r----+--_
47011

OOTPUT =t>-OOTPUT

47011

INPUTS

47011

(A) Equiva lent schematic.

(8) Corresponding symbol.

Fig. 1-3. Three-input RTL gate.

not receive base current. The four-input gate is used exactly as the two- or
three-input gate is used, except, of course, that it responds nals present on all four inputs. Whenever more than four inputs are needed on a logic gate, a gate ex pander is necessary. This is an Ie that provides enough extra input tran sistors
to to

the logic sig

bring a gate

to

the desired number of inputs. Two gate expanders

are shown in Fig. 1-5 along with their logic symbols. One, two- and four input gate expanders are readily available. Fig. 1-6 shows how a four-input gate expander may be used with a four-input gate to produce an eight input gate. Gate expanders may be doubled up as required to obtain any reasonable number of logic inputs. They are useful when conventional circuitry is interfaced with Ie's, and they also may be used to add extra "preclear" and "preset" inputs to certain flip-flops which will be discussed later.
+3.6VDC

64011

r----+------_
A

OOTPUT

0--""'-1-1
47011

47011

47011

INPUTS

47011

iV-OOTPUT
(A) Equiva lent schematic. (8) Corresponding symbol. Fig. 1-4. Four-input RTL g.te. 11

r-------jr--oO OUTPUT

4701l

4701l INPUTS

:j>_J
ISYMBOL)

I

(A) Two-input expander_
.-----..---.--__o OUTPUT

4701l

4701l

4701l

4701l INPUTS

ISYMBOL)

(B) Four-input expander_ Fig_ 1-5_ Gate expanders. A four-input gate may be converted into a three-input gate by ground

ing one input, into a two-input gate by grounding two inputs, and into a one-input gate (inverter) by grounding three inputs. Since several gates are usually available in each IC package, the total number of IC packages needed to o a job often can b jeduced. In any RTL circuit, all unused gate inputs should always be grounded. Failure to do so can lead to noise problems and erratic operation. It is also possible to tie two-input gates together at their outputs to pro duce a single four-input gate, or to use two three-input gates to make a six-input gate. Since this connection alters both the input drive require ments and the Output drive availability (it puts both collector resistors in parallel), it should be used with discretion. Connecting more than two gates together at their outputs is not recommended. Sometimes the effect of another gate input may be gained by selectively applying supply voltage to the entire IC package. This technique is called strobing and, in special cases, can produce the effect of an additional gate input on each gate in the IC package.

EC>r
D INPUT

OUTPUT

: Et> [
I I

(FOUR-INPUT GATEI

i

Fig. 1�6. Use of a gate expander.

F G H (GAIT EXPANDER)

I �

12

NC

+J.6VDC

1K

01

NC

470(l 00 TPUT INPUT 470(l

(A) Equivalent schematic.

(B) Corresponding symbol.

Fig. 1-7. One-input inverting buffer. Buffers A buffer is a higher-power IC used whenever many other Ie's have to be driven from a single source, or whenever a more powerful output signal is needed to drive external circuitry. There are several types of buffers. The simplest and most common have one input and invert the signal; thus they are nothing but high-power NOT gates, or inverters. This type of buffer is shown in Fig. 1-7. If the input is grounded, Q1 and Q3 remain off. Transistor Q2 then receives base current through the 640-ohm resistor, and the output terminal swings positive. If the input is made positive, base current reaches Q1 and Q3, and Q3 turns on, grounding the output. Since Q1 is on, Q2 receives no base current and stays off. The output stage actually operates in a push-push manner, forcing the output terminal to either a positive voltage or ground, following the commands of an input signal. The 1k resistor shown is internal to the buffer and is brought out to a separate pin; this resistor is normally left unconnected. In Chapter 3 it will be shown that by connecting this resistor to the positive voltage source and by capacitor-coupling the input, the buffer may be made into a relatively high-power pulse generator, useful for waveform shaping and generating reset pulses in IC systems. There are fancier forms of buffers that have more than one input. These allow input logic to be performed as well as providing a high-power out put. A two-input inverting buffer and a three-input noninverting buffer are examples of these fancier logic blocks. They appear in Figs. 1-8 and 1-9, respectively. JK

Flip-Flop

The JK flip-flop is a more complex IC logic block and is useful for per forming binary division, storage, counting, scaling, and other more com13

+J.6V

------

OOTT

NC INPUTS

UK

OOTT

UK

(A) Equivalent schematic.

(6) Corresponding symbol. .

Fig. 1-8. Two-input buffer.

plex forms of logic. It can divide by two without the need for other logic elements. JK flip-flops have four and sometimes five inputs, called the set, toggle, clear, preclear, and preset inputs, and two complementary outputs called the Q and "Q" outputs. The schematic and logic symbol of the JK
" "

flip-flop are shown in Fig. 1-10. Details of this particular logic block are contained in Chapter

5.
+J.6V

640Q 640Q
"'NC

lOOQ

OOTT

470Q

470Q

470Q

470(;
*SPECIAL-PURPOSE OOTPUTS

A B C

s:>=



ABSENCE OF OOTT IRCLE INDICATES NONINVERTING LOGIC BLOCK

OOTPUT

INPUTS

INPUTS

(A) Equivalent schematic.

(6) Corresponding symbol.

Fig. 1-9. Three-input noninverting buffer. 14

+3.6VOC +3.6VOC

640(l

Q
01 RECT
+3.6VOC 470(l 450(l PRESET

OUTPUT

Q

OUTPUT

01 RECT

PREC.lEAR

450(l

INPUT C.

INPUT S. (OPTIONAL!

+3.6VOC +3.6VDC

r
+3.6VOC +3.6VDC

I I

5 64O(l

'P

:!!

-

... :0;;



----------, I I I I I I I I Co O I

::I>
3OO(l 3OO(l

: 0
I f
450(l

640(l

1 11 I 1 1
640(l

1 0

(B) Corresponding symbol.

l'

SET INPUT

!

S

N
J.,.

f51

O(l

I

f
450(l

I

_ oo t

ClEAR INPUT C

TOGGLE

....

INPUT T

450(l

225(l

1
(A) One equivalent schematic.

The essential difference between the JK flip-flop and the simpler logic blocks is that a JK flip-flop runs in a clocked mode. Regardless of what is done to the set and clear inputs, nothing happens until the instant the signal on the toggle input abruptly drops from a positive voltage to ground. We say that the JK is edge sensitive to the negative-going toggle transition. This circuit action allows us to "set up" what the JK flip-flop is supposed to do independently of when it actually does it. This feature is particularly useful in shift registers, decimal counters, and other counter circuits. Type-D Flip-Flop The Type-D flip-flop is another version of a clocked logic block whose input commands, or conditioning, may be set up prior to the actual per formance of the logic. Externally, the Type-D flip-flop is very similar to a JK flip-flop, except that it lacks a clear input. It is used primarily for shift registers, arithmetic calculations, and storage circuits. The schematic and logic symbol for the Type-D flip-flop are shown in Fig. I-II. Details of this device are contained in Chapter 5.

MULTIPLE-FUNCTION IC'S Most of the available RTL integrated circuits combine two or more logic blocks in the same package, thus reducing the total number of packages needed for any particular circuit, and making maximum use of all available pins on the IC package. For instance, a dual two-input gate is an IC pack age with two independent two-input gates in the same package. Similarly, a quad two-input gate contains four independent two-input gates in the same package, and a dual four-input gate has two independent four-input gates in the same package. The only common connections between the gates are the positive source and ground. All the gates in a single IC may be used either together or in totally unrelated circuits. There is no cross talk problem. Other popular configurations are dual flip-flops, dual buffers, hex invert ers (six to a package), and triple three-input gates. Some special combina tions are also available, such as a JK flip-flop, an expander, and two buffers. These are particularly useful for reducing the total number of IC packages used in specialized applications. POWER LEVELS There are currently two types of RTL available, the medium-power RTL and the milliwatt, or low-power, RTL. These two types usually are similar in cost and differ primarily in the internal power dissipation. The internal power consumption is four to five times greater in the medium-power RTL than in the low-power RTL. For instance, the two-input gate of Fig. I-I is a medium-power gate. It has a 640-ohm collector resistor and dissipates
16

+3.6VDC

+3.6VDC

Q OUTPUT Q OUTPUT UK
01 RECT PRESET So

3.6K

3.6K

UK

DI RECT PRECLEAR Co + 3. 6 VOC +3.6VDC

+3. 6VOC

+3.6V

...

.

-

... "< "a

tI ::D

cp

t 0
+ + + + +
'!A

"!'

I I
UK (A) One equivalent circuit.

+

+

+
1.5K

+UK

'VA

UK

UK

j

CLOCKED SET 5

CLOCK INPUTT

,...----------I I I I I I I I I Co Q I

.....

(8) Corresponding symbol.

0

about 25 milliwatts with both inputs positive. The equivalent low-power RTL two-input gate has a 3.6k collector resistor and dissipates about 5 milliwatts with both inputs positive. Low-power operation is never obtained free. The low-power Ies have restricted operating speeds and very restricted drive capabilities. Often a circuit made entirely from low-power Ies requires more packages, since extra buffers may be needed to obtain sufficient drive levels. The choice of low-power versus medium-power RTL depends on the complexity of the circuit and the available power supply. The usual choice is to use the me dium-power RTL and save the low-power units for use when special design problems occur..

LOADING: FAN-IN AND FAN-OUT
All the transistors in the RTL logic blocks operate either in the saturated or cut-off mode; that is, the equivalent transistors are either completely conducting or completely cut off during steady-state operation. It is reason .able to expect that there is some minimum input drive level needed to pro vide enough base current to keep the input transistors saturated; similarly, there must be a maximum available output current for any IC The input current requirement is called the capability is called the

fan-in

of the circuit, and the output drive

fan-out

of the circuit.

Rather than worrying about delivering so many milliamperes into a transistor with such-and-such gain, a much simpler method is used in inte grated-circuit work. The manufacturer investigates the worst-case perform ance of his logic line and then assigns a

loading number

to each terminal.

re quired. A loading number of 15 on an output means that 15 units of drive are available. We can load an output with any combination of units less than or equal to the available output. For instance, one type of JK flip-flop
has a fan-out of 10. This output can be used to drive any combination of gates that total 10 units or less. Three medium-power gates would require 3 units of drive each, for a total of 9; we may safely connect these to the lO-unit output. If we added a fourth gate of fan-in 3, we would be trying to get 12 units from an output with a fan-out of 10, and the circuit most likely would not perforrri properly. The fan-out for any Ie should not be exceeded. This is particularly true of the low-power RTL. The fan-in and fan-out numbers for the low-power and the medium-power RTL are compatible. Thus, a low-power gate with a fan-out of 3 can drive a medium-power gate with a fan-in of 3. When the available fan-out is not enough, it can be "amplified" by an additional gate, inverter, or buffer. For instance, a low-power gate amplifies a 1 to a 3; a medium-power gate or inverter amplifies a 3 to a 16; a buffer amplifies a 5 to an 80. Buffers are particularly handy whenever several logic devices are to be driven in parallel. As an example, if ten flip-flops are to
18

A loading number of 3 on an input means that 3 units of drive are

(A) TO-5 package.

(8) In-line package.

Fig. 1-12. RTL integrated-circuit packages.

be reset simultaneously, 30 units of drive are required; if they are to be toggled simultaneously, 50 drive units are needed. There are two factors that may have to be considered when it is desired
to

amplify the fan-out. Almost all gates and buffers invert the input and

provide its complement at the output. Inversion in the final output can be avoided either by picking an input complementary to the desired one or by reinverting the output. A second possible problem is time delay intro duced as the signal goes through a gate or an inverter_ While this delay may be as little as 12 nanoseconds (billionths of a second) or so, it may become important in high-speed systems.

PACKAGES AND LEAD CONVENTIONS
Modern integrated circuits come in a wide variety of packages, but the low-cost industrial RTL versions are mostly limited to one of two multilead molded plastic packages, an eight-lead, TO-5 round package and a rectan-

B+FOR ALL RTL ALWAYS INTEGRATED CIRCU ITS

I
PIN CIRCLE.1OO" DRILL SIZE NO.6) FOR A CLEARANCE MOLNTING. USE A NOTCH& CODE DOT

PIN SPACING .100" PIN SEPARATION .300" DRILL SIZE NO.6) FOR A CLEARANCE MOLNTlNG. USE TWO

8

ALWAYS B+

1 I NO.1 DRILL. " FlAT&COLOR DOT

GROLND FOR ALL RTL INTEGRATED CI RCU ITS



3/32" x 3/4" SLOTS ON .300" CENTERS,

(A) TO-5 package.

(8) In-line package.

Fig_ 1-13. Ie pin information. 19

+3. 6V AT36 rnA (ALL Cl.ITPUTS LOW) MC789P HEX INVERTER MEDIUM POWER

+3.6V AT 12 rnA (BOTH OUTPUTS LOW) L914 DUAL TWO-INPUT GATE MEDIUM POWER

"" VIEW TOP

+3.6 V AT 24 rnA (ALL OUTPUTS LOW) MC724P QUAD TWO-INPUT GATE MEDIUM POWER

+3.6 V AT 12 rnA (BOTH OUTPUTS LOW) MC715P DUAL THREE-INPUT GATE MEDIUM POWER

+3.6 V AT 0 rnA (MUST BE CONNECTED) MC785P QUAD TWO-INPUT EXPANDER MEDIUM POWER (FAN-Cl.IT DETERMINED BY GATE BEING EXPANDED)

Fig. 1.14. Some available

20

+3. 6V AT 72 mA (BOTH OUTPUTS HIGH & LOADED) MC799B DUAL BUFFER MEDIUM POWER *LEAVE THIS TERMINAL UNCONNECTED EXCEPT FOR PUL SE GENERA TOR

+3.6V AT 36 mA

L900 NC BUFFER MEDIUM POWER if. UEAVE THIS TERMINAL UNCONNECTED EXCEPT FOR PULSE GENERA TOR. '=F"

+3.6V AT 44 mA

32mA*

MC790P & MC79IP* DUALJK FLIP-FLOP MEDIUM POWER

+3.6 V ATI2mA MC776P DUALJK FLIP-FLOP LOW POWER

+3.6V AT 100 mA (BOTH BUFFERS HIGH & LOADED) MC787P JK FLIP-FLOP, INVERTER, AND TWO BUFFERS

NOTE:

POWER REQUIREMENTS ARE WORST CASE.

D o

.

FAN ruT FAN IN

.

RTL integrated circuits.

21

gular dual in-line package with 14 leads. These packages are shown in Fig. 1-12. Both packages have their leads identified counting counterclockwise from the top, and most manufacturers use this top-view convention because it makes the schematic, layout, and logic diagrams nearly identical. From a practical standpoint, this uniformity simplifies circuit-board layout and troubleshooting. The TO-5 package has pin 8 identified by a flat, a tab, or sometimes a color dot on the package; the count proceeds counterclockwise around the package when viewed from the top. The dual in-line package is identified by a dot beside pin 1. The count then proceeds down one side and back up the other side, returning to pin 14 directly above pin 1. A code notch be tween pins 1 and 14 also aids identification. These numbering conventions are shown in Fig. 1-13. The supply-voltage connections are always the same for a particular package. On the round, eight-lead package, pin 4 is always ground; pin 8 is always B+. The 14-lead rectangular package always has lead 4 grounded and lead 11 connected to B+. This is true of all RTL IC's but is not true of other (non-RTL) logic families that may be supplied in the 14-lead rectangular package. RTL is offered in several lines, differing in temperature performance and tolerance limits. For experimental work, either the hobby/experimental or the "industrial" grade RTL normally is used. These types are relatively low in cost and are the most readily available. They have a specified operating range of +50 to +130�F. Fig. 1-14 gives details on IC's referred to in the circuit descriptions in this book. The integrated circuits of Fig. 1-14 are stocked by a number of electronic distributors. The prices of IC's vary from unit to unit. The package price might be on the order of from one to three dollars in single quantities, depending on the complexity of the internal�circuitry. Always obtain a complete set of data sheets before you begin any IC work. These sheets serve as a road map of what can and cannot be done with integrated circuits, what their temperature restrictions are, their fan-in and fan-out, their power requirements, and their pin connections.
MOUNTING TECHNIQUES

There are several practical ways to mount RTL IC's. Those of greatest interest to the technician and the economy-minded experimenter are sock ets, standoffs, and PC methods.
Sockets

Sockets are handiest when the IC's have to be reused, but they are often expensive, and the close lead spacing often requires some fancy and fine wiring work. Sockets for IC's are usually a distributor stock item, and may
22

vary in price from less than $1 to $12 or more each. Usually the more ex pensive ones are made of Teflon and are intended for miliary use. For simple systems, the cost of sockets can be a significant portion of the total project.

Standoffs
One simple way to mount an IC is to bend the leads radially outward and solder them to a grouping of eight or fourteen Teflon-insulated stand offs pressed into a glass-fiber or phenolic board. This method spreads the leads for easy wiring or testing, and it makes the IC easy to change. Fig.

1-15 shows this mounting technique. Both the standoffs and the Ies are
easily reusable.

Fig.

1�15 .

.

Ie

mounted standoffs.

with

insulated

If the Ies are mounted right side up, the pin count will proceed counter clockwise, and the final wiring should correspond bering.
to

the data-sheet num

Printed Circuit Boards
Ies were designed for permanent insertion into printed circuit boards of the multilayer type. For simple circuits and digital instruments, single sided PC boards with jumpers are an attractive alternate. Kits are available that permit making your own PC boards, using either the acid-resist or the photographic method. Also, it is practical to use a "universal" PC master pattern with a group ing of IC land patterns that has only B+ and ground connected; connec tions can be made to the other terminals as necessary. These boards are commercially available and are reusable.
23

TOOLS
All of the conventional electronics hand tools carry over for Ie work, al though the smaller 4Y2-inch "jeweler's" diagonal cutting pliers and needle nose pliers are preferable
to

the larger "electronic" pliers. Several additional

tools are necessary for Ie work:
1. Syringe-type desoldering tool for removing Ie's and correcting wir-

ing errors.
2. Wire cleaner for desoldering tool.

3. Pocket magnifier for inspecting solder connections. 4. Knife for cutting circuit-board connections, separating solder bridges, and similar uses. 5. Toenail clipper for close cutting of soldered leads on printed circuit board. 6. Machinist's scriber for general probing. 7. Small vise or other way of holding circuit boards securely for close-in work.
8. Hand drill or miniature drill press. Most Ie's require a No. 67 hole

for each lead; larger components require a No. 60 hole. Drills of these small sizes cannot last long in a hand-held Y4-inch electric drill, even if the chuck will close down tightly enough to center them.

9. Pin vise and No. 67 drill for PC-hole cleaning and rework. SOLDERING
Always use a small soldering iron rated at 40 watts or less and very fine solder when soldering Ie's in place. While the Ie's themselves can with stand any reasonable amount of heat, problems with solder bridging, foil lifting, and poor joints increase when larger irons are used. Soldering guns are awkward for this kind of work and should not be used. A temperature controlling iron stand is a handy accessory if a great deal of Ie work is to be done. Be certain to double-check the Ie connections before soldering. It is so easy to put the Ie in upside down, to rotate it a lead or two, or worse yet, to put an Ie in the wrong place. To remove an Ie, use a syringe-type desoldering tool, and carefully re move all the solder from each lead, one at a time. Then carefully pry up the IC It should pop loose safely with no trouble at all.

POWER REQUIREMENTS
All the Ie's of Fig. 1-14 are rated to operate from a 3.6-volt de supply. In reality, most gate-only circuits will operate properly from a supply of 1.5
24
to

4.5 volts dc, and the more critical circuits using flip-flops will operate

from a supply of 3.1 to 4.1 volts dc. This voltage is easily obtained from batteries or from a low-voltage, high-current line-operated supply. Whatever power source is used, it is absolutely essential that proper high-frequency bypassing be provided for the IC's. This bypassing may be accomplished by placing a O.I-,uF and a 100-,uF capacitor in parallel at the
Ie end of the power-supply runs. The shortest possible leads should be used

(Fig. 1-16). It is also important to use large leads (or wide foil runs) for both the B+ and ground connections to minimize noise effects. The choice of batteries versus line operation depends on how many IC's are to be used, how portable the finished circuit must be, and whether the extra expense of a low-ripple power supply is justified. The first step in this decision is to calculate the current and power requirements.
USE ONLY HEAVY LEADS ORWIDEfOlL PlACE THESE CAPACITORS AS CLOSE TO IC'S AS POSSIBLE. USE MINIMUM LEAD LENGTHS.

POWER SUPPLY OR BATTERY
.1 F

I

IC DEVICE

CASE GROUND AT ONE POINT ONLY

Fig.

1-16.

High-frequency

by-passing of power leads.

CURRENT REQUIREMENTS
Table 1-1 shows the approximate average current drain for each logic block. To obtain the total current requirement, just add the currents for the individual elements. For instance, suppose we design a circuit that has three dual flip-flops, one dual buffer, and one dual two-input gate, all of which are medium-power RTL. The total current will be: 6 flip-flops at 22 rnA 2 buffers at 42 rnA 2 gates at 6 rnA Total 132 rnA 84 rnA 12 rnA 228 rnA

Thus, our supply would have to provide about 228 rnA. To be on the safe side, we would design around a 250-mA supply. The total power require ment would be equal to the supply voltage multiplied by the supply cur rent, or in this case 3.6 volts X 228 rnA about one watt. Note that a large number of flip-flops or buffers always means a large supply current. Thus the more complex Ie circuits will be quite difficult to power with batteries.
=

820 milliwatts, or, nominally,

BATTERY OPERATION
Ordinary flashlight cells, either two or three to the holder, may be used with many Ie circuits, provided they are properly bypassed, and provided
25

Table 1-1. Current Requirements for Logic Blocks
LOGIC BLOCK Medium-Power RTL
Inverter Gate Buffer 6 6 42 22 0

CURRENT (rnA)"

JK

Flip-Flop

Expander

Low-Power RTL
Gate Buffer 1 9 6 6

JK

Flip-Flop

Type-D Flip-Flop "With 3.6-volt dc supply (approximate values)

they can supply enough current for a long enough time. If the batteries are to last longer than about five hours, the maximum current drains listed in Table 1-2 should not be exceeded. Note that for circuits that take more than about 150 mA, the heavy-duty D cells or the more expensive alkaline cells must be used. For more details on battery life versus current drain, consult any of the handbooks published by many of the leading battery manufacturers.
Table 1-2. Maximum Current Drains
Type of Cell "AA" (carbon-zinc) Flashlight "c" (carbon-zinc) Flashlight "0" (carbon-zinc) Heavy-Duty "0" (carbon-zinc) Heavy-Duty "0" (alkaline)
Flashlight

Current (rnA)
30 90 150 200 300

One way to extend the life of the larger cells is to add a two-diode "bat tery-saver" selector switch, as shown in Fig. 1-17. When the switch is in the FRESH position, the battery will measure 4.5 volts, and the two 0.6-volt forward drops of the silicon diodes will produce a 3.3-volt output. As the battery ages, the switch is changed first to the NORMAL position, and finally to the OLD position, retaining about 3.3 volts at the output, even with the cells discharged to 1.1 volts each. With this technique, battery life may easily be doubled. Another, somewhat expensive, alternative is to use rechargeable nickel cadmium cells. Three 1.2-volt D cells nicely add up to 3.6 volts, and may be recharged many times. The 2000-mA-hr/200-mA-rate cell is suitable for many large projects.
26

I AMP50 PIV DIODE

..
IN4001


ALKALINE "0" CELLS

OFF

IN4001 111 FRESH 3.3VDC

3 HEAVY-DUTY OR

11

r ::

Fi

NORMAL

----

OLD

I
.----1---0
+

t
Fig. 1-17. "Battery saver" circuit.

When indicator lamps are used with the Ie's, their current requirements must also be taken into account. Dry-battery operation is usually imprac tical in any circuit with more than three indicator lamps in addition to the IC load.

LINE OPERATION

Ac-line operation requires immense electrolytic capacitors, a regulator, or both to obtain the low ripple at high current levels required for IC work. The elegance of the required supply increases with the current require ments and the complexity of the actual IC circuit. For a circuit using Ie's only and no indicators, with a total current drain of less than 500 rnA, the brute-force filtered supply of Fig. 1-18 may be used. The circuit includes a conventional filament transformer, two silicon diodes, and a large-value electrolytic capacitor. The immense capacitance is required in order to provide a low ripple at high current levels. Com puter-grade electrolytic capacitors of this size are priced in the under-five-

Tl 6.3 VAC 1-AMP

--c:J} ..
IN4001 500 mA MAXIMUM 3.6 VOLTS

1l0V

---/
6()Hz


FILAMENT

TRA NSFORMER

+
IN4001111 I AMP50 PIV DIODE IDDOF CI 6 VOLTS TO I' CIRCU IT

BLK

.IF

CASE CONNECTION

FOR A loo-mA MAXIMUM SUPPLY, REDUCE Tl TO I AMPERE & CI TO 4000F.

Fig. 1-18. Filtered dc power supply. 27

---c:::J}--
lN4001

rv rv
MDA942-1

+

oK"

I


BLK


L
6.3-VOLT, 2-AMP FILAMENT TRANSFORMER

.1

I

I '""
18000 F (3) lN4001

+6V OI

: :TOR
O 6V,1 AMP

_____



lOY
______

J

I,S-AMP, I-PHASE, FULL-WAVE BRIDGE MODULE MDA942-1

I.MM'

+J.6V

0 Ie POWER 3.6 V .5 AMP
,1 F

Fig. 1-19. Dual-voltage de supply.

dollar range and measure about 1 Y2 inches in diameter by 5 inches long. A two-voltage, brute-force filtered supply is shown in Fig. 1-19. Here, 3.6 volts dc at 500 mA or less and 6 volts at 1 ampere are provided. This type of supply is ideal for IC projects which include indicator lamps. Fig. 1-20 shows a regulated supply that uses relatively small-value elec trolytic capacitors and that will provide 3.6 volts at 1 ampere. For applica tions requiring higher current, this supply may be "beefed up" with larger rectifiers and filters, and a bigger power transistor.



I OV 60 Hz

;

-elN47Jl BLK

rv "v
MDA942-1

+

'01

....0.,/

/-e{' o� ;

2N3766 (BOTTOM VIEW)

o



3JOQ

2N3766 (ON HEAT SINK)

BLK 12,6-VOLT, 2-AMP FILAMENT TRANSFORMER 1. S-AMP, !-PHASE FULL-WAVE BR I DGE MODULE MDA942-1

+

Fig. 1-20. Regulated de power supply.

"BAD" AND "BURNED OUT" INTEGRATED CIRCUITS
There are countless examples of IC work in which, if the circuit did not operate on the first try, the Ie's were immediately blamed and considered "bad" or "burned out." In reality, RTL Ie's are almost indestructible, and
28

the likelihood of getting a defective new one is very slight. The Ie's are neither heat nor static sensitive and will withstand considerably more than normal soldering heat. So long as circuit voltages are less than 5 volts or so, the IC will withstand virtually any combination of shorted or reverse polarity connections without failure. The real gremlin is not a bad IC, but sloppy or careless workmanship solder bridges between connections, poor soldering, reverse supply polarity, a PC layout error, the wrong IC in the socket or the IC in upside down or rotated one pin, a PC board layout done bottom-view and the Ie's inserted top-view (reversing all the connections), or the omission of high-fre quency supply bypassing. These are the real problems in most IC circuits and account for practically all circuit problems. Be sure
to

watch for them.

29

CHAPTER

2

Logic and Switching Circuits
Digital-logic gates often are used as high-speed electronic switches. They also are used to respond to the coincidence or absence of input signals to follow a set of logic rules. In this chapter, the logic gate as a switch will be emphasized-how to use it, what rules to follow, and how to design any desired switching function with digital-logic gates.

THE TWO-INPUT GATE AS A SIMPLE SWITCH
Suppose we wish to turn a train of pulses on and then turn them off again under command. For instance, we might like to allow high-frequency pulses to enter an electronic counter for precisely one second. The readout of the counter would then indicate the total number of pulses present dur ing the second, or the frequency of the input in pulses per second. To do this, a two-input gate may be used as in Fig. 2-l. So long as the switching waveform (input B) is positive, the output of the two-input gate will stay grounded. If terminal B is grounded, the two input gate will respond to the signal waveform (input A), and an inverted replica of input A will appear at the output. Pulses will appear at the out put only when input B is grounded. Thus the gate serves as a simple elec tronic switch. If we would rather control the switch with a positive-going waveform, we may simply add an inverter to input B. This circuit is shown in Fig. 2-2. Here, the input signals at A are passed and inverted only if terminal B is positive; the signals are blocked if terminal B is grounded. In Fig. 2-3, an inverter has been added to input A also. Now, pulses are passed "right side up" only when input B is positive. This circuit could be built with a dual two-input gate and two inverters, or with a quad two-input gate by itself. If the one-package quad two-input
31

INPUT A

INPUT A INPUTB


_

ISIGNALI INPUT B OUTPUT (SWITCHING COMMANDI OUTPUT

-.JLJLJlJLIL +3
----, r-

0



+3 0 3

(A) Diagram.

+O
(B) Waveforms.

Fig. 2�1. Two.input gate used as switch.

gate is used, two inputs are grounded to give the required two inverters, one gate is used "as is," and one is left over for use elsewhere. This form of electronic switch is useful when it is desired to turn a digi� ral signal on or off electronically, or when it is desired to from dc to hours.
INPUT A 0

sample

a portion

of a digital signaL RTL electronic switches may be operated at frequencies

10

MHz, and at speeds between

50

nanoseconds and many

r--

OUTPUT

INPUT A nn n nn +3 (SIGNALI --l L..J L..J L..J LJ L 0 (S T I G COMMAND) OUTPUT

INPUTB

0 J

(8) Waveforms.

+

+3 o



(A) Diagram.

Fig. 2�2. Electronic switch for positive input.

There are some features of the simple electronic switches discussed so far that might not be desirable in some special applications. The switch may be turned on either just before or just after the instant a pulse arrives on input A. If we watch the switch output from sample to sample, we would obtain a roundoff error of plus and minus one count. In an electronic counter, this would make the last digit fluctuate. Also, the switch might be turned on

during

an input pulse; the output would then contain part of a

pulse. If the time

width

of each pulse at input A is critical later on in the

circuit, the switching will introduce a timing error. To get around these problems, it is necessary to resort to a slightly more complex circuit described in Chapter
INPUT A

synchronized 5.

electronic switch, a

OUTPUT

INPUT A (SIGNALI INPUTB

JL.J1Sl.JLJL +3

0 0

) NPUTB

(SWITCHING COMMAND)

+3
nnn

ouwm



LJ

LJ



+3

0

(A) Diagram.

(8) Waveforms.

Fig. 2�3. Noninverting electronic switch. 32

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