Scientific Development Corporation Minivac 601 User manual

Getting acquainted with
M i n i v a c 6 0 1
SCIENTIFIC r. j |
DEVELOPMENT 3 T ir S t S te p
corporation toward the exciting world of electronic
w— data processing via digital computers

I he MIN I VAC 601 computer and
this book are used together to demonstrate
the operation of digi+a computer components
and to teach princip es basic to their use.
As you become fami iar with M INIVAC 601
and understand its re ationship to arge
digita computers, you wi be performing
the operations basic to a modern e ectronic
data processing machine.
This is the first in a series of books
using M INIVAC 601 to demonstrate the
fundamenta s of modern digita computers.
This book acquaints you with M INIVAC 601 .
The second book in this series re ates
the components of M INIVAC 601 to
corresponding parts of a arge commercia
digita computer. Other books enab e
you to use M INIVAC 601 to discover
how these parts function to make
decisions, to do arithmetic, and
to do practica work for men. A
book of games which may be
p ayed with M INIVAC 601
is a so provided.
CONTENTS

I ) POWER SUPPLY ......................................................................................... 3
7.) PROGRAMMING WIRES ....................................................................................................... 4
C osed Circuit' Princip e ........................................................ 4
Using the Programming Wires ............................................. 4
Experiment 1: Use of Programming Wires ................... 5
Wiring Shorthand ......................................................................... 5
3fc) LIGH TS . ...................... 6
Experiment 2: Sing e Light Operation ....................... 7
■ 4 ) PUSHBUTTONS...................................................................................................................... 8
Experiment 3: Pushbutton Operation ........................... 9
Experiment 4: Series C ircuit ........................................... |q
Experiment 5: Para e Circuit ............................................ u
5) RELAYS ...................................................................................................................... 12
Experiment 6: Manua Re ay Operation. . . ............ 13
E ectrica Operation of the Re ay ..................................... 14
Experiment 7: E ectrica Re ay Operation 15
Experiment 8: One Re ay Contro s Another ..........
Experiment 9: A Re ay Contro s Itse f ........................... 17
PAGES
__ ___ESP(i5Pi
f SLIDE
SW ITCHES. .......................... * ............ . ......................... . ........................... 18
Experiment 10: S ide Switch Operation ........................ 19
'ROTARY SWITCH...................................................................................................................... 20
Experiment 11: Manua Operation of
Rotary Swi tc h ......................... 21
Motor Drive ....................................................................................... 22
Resistors ............................................................................................ 22
Decima Input-Output ........................................................... 22
Experiment 12: Basic Motor Operation .................... 23
Experiment 13: Motor Driven Rotary Switch. • • • 23
Pu se Generator ......................................................................... 24
Programmer .................................................................................... 24
Experiment 14: Motor Reversing ........................................ 24
8) M ATRIX ..................................................................................................................... 25
9) AUXILIARY TERMINALS ........................................................................................... 25
1 0 ) LO O KIN G AHEAD WITH M INIVAC 601 ................................................................................................................ 26
Summary: Book 1 ...................................................................... 26
Book II: What is a Digita Com puter? .................... 26
Book III: How Computers
Make Logica Decisions 26
Book IV: How Computers Do Arithmetic ................. 27
Book V: How Computers Work for Man .................... 27
Book V I: MINIVAC Games ................................................... 27
PROBLEMS FOR M INIVAC 601 ........................... 28
to 32

The Mini vac Manua was prepared and edited by the staff of
Scientific Deve opment Corporation
First Printing—August, 1961
EX LIBRIS ccapitalia net
Copyright (c\ 1961 by Scientific Deve opment Corporation, 372 Main Street, Watertown, Massachusetts

POWER SU PPLY
he power supp y converts the 110-vo t AC power obtained
from a standard e ectric out et in your home to a safe working
eve of 12 vo ts DC. This ow vo tage DC is used to
power M INIVAC and is connected to a termina s +
and - on the power pane . Most toy e ectric trains
use the same ow-vo tage power as M INIVAC and
therefore working with the MINIVAC is as safe as
operating an e ectric train.
The POWER SWITCH is
used to turn power ON and OFF.
The power shou d be OFF when
ever you are wiring the
computer. Fo owing this
practice w i estab ish good
working habits and wi he p
to prevent accidenta short-
circuits. The power must be
turned OFF when the computer
is not in use. The red power ight
shows when the power is O N .
The red button above the power switch abe ed CIRCUIT BREAKER*
is a safety switch which automatica y turns off the power supp y
when it is over oaded. An over oaded circuit or a short-circuit
wi cause the circuit breaker to "b ow" just ike a househo d
fuse. A short circuit occurs when + is wired direct y to -
without a component in between. The power supp y
may be restored to norma operation after a short-
circuit by changing the fau ty wiring and then
pushing the red circuit-breaker button back in.
CAUT/o n :
Do NOT ho d the circuit-
breaker button in if it
continues to "b ow." Turn
power off and determine the
cause for drawing excessive
current before proceeding
with the experiments.
N ow ... .p ug the POWER CORD into
a standard 110-vo t AC (NOT DC)
out et, and you are ready to
GET ACQUAINTED
WITH M INIVAC 601 ...........
3

w
2PROGRAMMING W IRES
^Programming wires of different engths are provided to make e ectrica
( programming) connections between various termina s on M INIVAC 601 .
These wires estab ish c osed e ectrica circuits and route the current through
one or more components to create a desired computer circuit.
Each component in the computer
is connected to nearby termina s
by permanent connections made
under the computer pane .
The components may be interconnected by
inserting programming wires into the termina s.
Each termina has two ho es side-by-side which
are connected together underneath the computer
pane . Programming wires may be p ugged into
either (or both) ho es of the termina . A
programming wires are co or-coded by ength.
CLOSED CIRCUIT PRINCIPLE
For any e ectrica device to operate, it is
necessary for e ectrica current to f ow
THROUGH the device. A c osed e ectrica
circuit must be estab ished to et the
e ectrons f ow from the negative power
supp y termina ( - ) through the
component to the positive power supp y
termina ( + ). Thus, a e ectrica
components on the M INIVAC 601 require
at east 2 connections to operate.
AElectrons our
Electrons IN
USING THE PROGRAMMING WIRES
The programming wires are used to connect
various components of M INIVAC 601 . C osed
circuits are wired through the termina s provided
on the conso e for each component. Each
termina is identified by a etter printed be ow
it, and by the number printed at the
top of the section in which it is ocated.
This makes possib e easy identification of
termina points when wiring components
together in future experiments. We are
now ready to use the programming wires.
4

EXPERIMENT |
OF PROGRAMMING WIRES
his experiment demonstrates the use of programming
wires to make connections on MINIVAC 601 .
y Take two programming wires. Grasp one
end of the first wire firm y between your
thumb and forefinger.
Connect this end of the programming
wire to termina 1+ on the
computer pane by pushing
it into one of the two ho es
just be ow the + in section 1
of the computer.
3 ) Take the other end of this program
ming wire and connect 1+ to
termina 1A by pushing it
into one of the two ho es
just above the etter A in
section 1 of the computer.
^ /S im i a r y, connect termina 1 B to
termina 1- with the second programming
wire. These connections cause amp 1
to ight when the Power Switch is turned on.
This simp e circuit is discussed
further in Experiment 2.
Disconnect the programming wire by pu ing both ends from the
computer termina s. Do NOT disconnect the program
ming wires from the conso e by pu ing on the wire
because the wire may break. A programming wires
shou d be disconnected after each experiment or prob em.
WIRING SHORTHAND
A W IRING SHORTHAND is used to indicate connections which are to be
made on the computer by simp y writing the two termina designations
with a s ash in between. In Experiment 1, termina 1 + was connected
to termina 1A. This is written in shorthand -------- — ■ , /
A series of such shorthand wiring instructions wi be given to ' / 1/^
describe the wiring of a comp ete circuit.
5

< identica ights Iabe ed
"Binary Output" are used in
M INIVAC 601 to show what is
happening in various parts of the
computer. A ight w i come on when
is connected in a c osed circuit so
rrent f ows through the ight.
This a ows the computer to te an operator what
it is doing and to disp ay the answer to a computer prob em,
Each ight is identified by the section
number direct y above it.
In order for a ight to turn ON (to ight),
current must f ow THROUGH the ight.
The e ectrons must f ow IN on one wire
and OUT on another wire. This is the
c osed circuit princip e for ights.
The termina s abe ed A and B on either side of
each ight are used to supp y the e ectrica
power to turn the ight O N . A ight comes
ON when termina A is connected to one
power supp y termina ( + or - ) and termina
B is connected to the other power supp y termina ( - or + ).
When the circuit is
OPENED
fhe light is OFF
l^o Connection
U § h t
off
When the circuit ig
CLOSED
the lig/nt comes ON >o )
* \ V '
* \

— I
EXPERIMENT 2
1+
I -
SINGLE LIGHT OPERATION
his experiment demonstrates the operation of
a sing e binary output ight.
i; Using two short programming wires,
make the connections 1+/1A and 1- / 1B.
Turn the power switch ON (be sure
the main power cord is p ugged into a
proper out et). Light 1 comes O N ’
because current f ows through the ight.
V
1A
Turn the power switch OFF and
disconnect the programming wires.
Power shou d be turned OFF and
a programming wires shou d be
disconnected after each experiment
is comp eted.
V Any of the ights may be operated by
connecting programming wires from + to A
and from - to B just as was done for ight 1.
Make connections to two or more ights at once.
IB (The circuit diagram ooks ike this)
The ights are used in ater experiments to
represent numbers. The ight OFF wi represent
a zero ( 0 ) and the ight ON wi represent a one ( 1 ).
The numbers zero ( 0 ) and one ( 1 ) are the on y numbers
used in the binary number system, and it is for this
reason that the ights are abe ed "Binary Output."
Binary numbers and their use in digita computers
be taken up ater.
Binary Number System
0FF= 0
' " • v
S L ■
0 N = |
W
7

PUSHBUTTONS
he section of the computer pane abe ed "Binary Input" contains
six identica pushbuttons which are used by the operator to supp y
information to the computer. The pushbuttons may be used to te the
computer what to do, or to indicate the va ue of input numbers.
Pushbuttons may be used to contro the other components of M INIVAC 601
Each pushbutton is identified by its section number on the computer pane .
Each of the six binary input pushbuttons has three termina s ocated direct y
above it on the computer pane . Each termina is connected under
the pane to a contact. The termina s are abe ed X , Y and Z .
The three contacts for each of the six
pushbuttons are a connected to termina s in the same manner:
When the pushbutton is UP, an e ectrica
connection is made between termina s Y
and Z . When the pushbutton is DOWN,
the e ectrica connection is switched to
termina s Y and X . Termina Y is connected
to the "common" contact and is a ways used when
the pushbutton is connected in a circuit.
When a pushbutton is shown in a circuit
diagram, the contacts are ALW AYS shown
with the pushbutton UP - in the "norma y
c osed" (N .C .) position. Notice that
termina s X and Y are not connected when
the pushbutton is UP, and that termina s
Y and Z are not connected when the
pushbutton is DOW N.
up= y z
i r :
j!*2.
Dowm=x/y
The fo owing experiments demonstrate basic circuits in which
one or two pushbuttons are used with a ight.
♦ N

EXPERIMENT 3
PUSHBUTTON OPERATION
St..
I I his experiment uses a ight to demonstrate the operation of a pushbutton
Both norma y open and norma y c osed circuits are connected.
>)
* )
3)
«)
6)
7)
s\
1+j x
-*—
The norma y open pushbutton- ight
circuit drawing ooks ike this:
Program this circuit by making
the fo owing connections: 1+/1Y, 1)(/1A, 1-/1B
Turn the power switch ON. Push DOWN on pushbutton 1. Light comes ON because the
circuit from + to - is c osed through the pushbutton contacts and through ight 1 .
I -
Re ease the pushbutton and the ight goes OFF. The ight goes OFF because the circuit
from + to - is open (broken) by the pushbutton contacts. Turn the power switch OFF.
1Z
With a norma y c osed pushbutton- ight added, ^ -
the circuit drawing ooks ike this:
Program this by adding connections — 1Z/2A, 2B/2- ^
IX
1A
IB
Turn the power switch ON. Light 2 comes on as soon as power
is turned ON. Light 2 ights because the circuit from + to -
is competed through the norma y c osed contact (Z) of pushbutton 1 .
Push down on pushbutton 1 . Light 2 goes OFF and ight 1 comes ON.
Light 2 goes OFF because the circuit is opened by the switch and
e ectric current can no onger f ow. Light 1 comes ON because the
circuit is c osed through the switch.
Push up and down s ow y on pushbutton 1 and carefu y watch the
operation of the two ights. One ight a ways goes OFF before the other
ight comes ON. There is a position, with the pushbutton on y part y
depressed, where both ights are OFF. Try to find this position. The
switch breaks one connection before it makes the other connection. The
pushbuttons are thus ca ed "break-before-make" switches. This is important because it
shows that the norma y open contact is never connected direct y to the norma y c osed contact,
even for a very short time. This feature is necessary for the proper operation of some MINIVAC circuits.
2A
2B
I - z -
This experiment demonstrates the two basic ways to use a pushbutton. The norma y c osed contact
(Y/Z ) may be used to comp ete a circuit when the pushbutton is UP, and the norma y open
contact (X/Y) may be used to comp ete a circuit when the pushbutton is DOWN.
The pushbuttons wi be used in ater experiments to
represent numbers. The pushbutton UP wi represent a
Zero (0), and the pushbutton DOWN wi represent a one (1).
The numbers, zero (0) and one (1) are the on y numbers
used in the binary number system. and it is for this
reason that the pushbuttons are abe ed "Binary
Input." Binary numbers, and their use in digita
computers, wi be taken up ater.
Binary fdunnber Syste
_ l
UP=0" DOWN = 1
*<■//

EXPERIMENT 4
SERIES CIRCUIT
I his experiment demonstrates the use of
two pushbuttons connected together in series
to form a circuit where both pushbuttons must be
pushed at the same time before the circuit is c osed.
0 Program this circuit by making the
fo owing connections: 1+/1Y 2>y2A
1V2Y 2B/2-
Turn the power switch ON and push down
pushbutton 1 . Watch ight 2. It does NOT
ight because the connection from + to
the ight is broken by pushbutton 2.
3/ Re ease pushbutton 1 and push down push
button 2. Watch ight 2. It sti does NOT
ight because the connection from + to
the ight is now broken by pushbutton 1 .
4) Push down both pushbutton 1 and
pushbutton 2 at the same time and see ight
2 go O N . A comp ete circuit is now
made through both pushbuttons.
It is possib e to connect more than two push
buttons in series and make a circuit where aM the
pushbuttons connected must be pushed down before
the circuit is comp eted. Construct a series
circuit using three or more pushbuttons by your
se f, to demonstrate this princip e. The circuit,
with termina numbers indicated, shou d first be
drawn on paper. The circuit shou d then be
connected on the computer using programming wires.
The circuit diagram ooks ike thi
1Z 2 Z
l + * A -
_________
iy i x vi
AN "AND" CIRCUIT — The series circuit, where two or more
pushbuttons must ALL be c osed to make £ comp ete circuit, is ca ed
an AND circuit, because both pushbutton 1 AND pushbutton 2 must be c osed
before the circuit is comp ete. This is a basic circuit of computer
ogic which wi be used ater.

EXPERIMENT 5 !
PARALLEL CIRCUIT
his experiment demonstrates the use of two
. I pushbuttons connected together in para e to
form a circuit where either pushbutton may be
pushed to comp ete the circuit.
I ) Program this circuit by making
the fo owing connections: 1+/1Y
1 V I A
1B/1-
VY/2Y
2V1X
Turn the power switch O N . The
ight does not come on because there
is not a c osed circuit.
3)Push down pushbutton 1. Light 1 comes
ON because a c osed circuit from +
through the ight to - is now made
through the norma y open
contact (IX ) of pushbutton 1.
4)Re ease pushbutton 1 and push
down pushbutton 2. The ight again
comes ON because a c osed circuit is
now made through the norma y open
contact (2X) of pushbutton 2.
5) Push down both pushbutton 1 and pushbutton 2 at
the same time. The circuit is c osed and the ight
comes ON if either pushbutton 1 is down OR if
pushbutton 2 is down OR if both pushbutton 1 and
pushbutton 2 are down at the same time. 1^0.
6) More than two pushbuttons may be connected in
para e to make a circuit where any one of the
pushbuttons may be pushed down to comp ete
the circuit. To demonstrate this princip e, construct
a para e circuit using three or more pushbuttons.
Draw the circuit diagram, and then connect the circuit
on the computer using the programming wires.
The circuit diagram ooks ike this:
12
1Y IX
« ♦
2Z
1A
0
• IB
2 *
AN "OR" CIRCUIT — The para e circuit, in which c osing either
of two or more contacts comp etes the circuit, is ca ed an OR
circuit. Pushing down either pushbutton 1 OR pushbutton 2
comp etes the circuit. This circuit is basic to much of the
computer ogic which is used ater.
I -
11

ch f ows Through the re ay co i , whereas the
pushbuttons are manua y operated.
The re ay is particu ar y usefu because it can
be connected so it wi "remember" whether it is ON or
. O FF. Every computer has some device which is ab e
"remember." In MINIVAC 601 this device
^ i s the re ay. The re ays may be used
X s-*. to contro any of the components
used in M INIVAC 601 .
££LA/ : / X .
VsmCwberiroJ1
device
Each of the six re ays has six termina s
ocated direct y be ow it on the computer pane
These termina s are connected under the computer
pane to contacts of the re ay switch. The
termina s are abe ed: G ,H ,J , & K ,L ,N .
RELAY ON
RELAY OFF
^ ix identica re ays abe ed
"storage-processing" are used by M INIVAC 601 to store or "remember"
and to process computer information. Each re ay has two sets of contacts,
simi ar to the pushbutton contacts, which open and c ose
together. The re ays are operated by an e ectric current
When the re ay is OFF, separate e ectrica con
nections are made between termina s H and J and
termina s L and N. When the re ay is ON,
separate e ectrica connections are made between
termina s H and G and termina s L and K.
When re ay contacts are shown in a circuit
diagram, the contacts are ALWAYS shown with the
re ay OFF. Notice that termina s H and Gand
termina s L and K are not connected when the re ay
is OFF. A so, termina s H and J and termina s L
and N are not connected when the re ay is ON.
The MINIVAC re ays are
mounted on the computer
pane with the contacts of
the re ay switch visib e. The
re ay arm is in the midd e,
between the other two contacts.
Termina s are connected
to the contacts ike this:
P asty Crossbar^)
j Arms on
Inorma/ly
closed
contacts
6 H J 14 L N
^Term ina s/
The two arms (H & L) are connected together.
Both contacts a ways c ose together.
The re ay switch contacts are connected to
termina s in the same pattern used with the
pushbutton contacts. The norma Iy-open (N .O.)
contact is connected to the eft termina , the
re ay arm (common contact) is connected to the
center termina , and the norma y-c osed (N .C.)
contact is connected to the right termina . The set
of contacts c oser to the operator is connected to
the set of termina s c oser to the operator.
The two re ay arms are connected together
mechanica y with a p astic crossbar. Both arms
move together and make or break contact at the
same time. Observe the re ay operation by
gent y pushing on the p astic crossbar with your
hand. Notice how the arm eaves the norma y-
c osed contact and swings over to touch the
norma y open contact.

EXPERIMENT £
MANUAL RELAY OPERATION
mis experiment uses two ights to demonstrate
the basic operation of a re ay switch.
> Connect the contacts of re ay 1
/ to turn ight 2 ON when the re ay
is OFF, and to turn ight 1 ON when
the re ay is O N .
for this circuit is
1G /1A
2B/2-
Turn power O N .
Light 2 comes ON
A.) Gent y push the re ay crossbar
to the eft. Light 2 goes OFF and
ight 1 comes O N . Watch the re ay
arm a ternate y touch one contact
and then the other as the re ay
crossbar is moved back and forth.
The circuit ooks ike this
1G 1A IB 1 -
13

5 Electrical Operation of the Relay
covfO
gif U n ike the pushbutton which must be operated manua y, the
re ay can be operated e ectrica y. Each re ay has a round
white co i , ocated to the eft of the arms. This is an e ectro
magnet which becomes magnetized when e ectric current f ows
through the co i . When the coi becomes "energized," the e ectro
magnet attracts the meta bar connected to the arms (by the p astic
crossbar) and pu s it to the eft. Sending current through
the coi of the e ectro-magnet operates the re ays.
— Thus, the re ay may be operated e ectrica y without
touching it physica y, but the pushbutton must
be operated manua y.
^ The re ay is turned ON by connecting the re ay coi in
a c osed e ectric circuit. When the circuit is c osed current
OO f ows through the coi and the coi is "energized."
Terminals fv opera-he
i Relay
Swi ches ———
jm m .
j /
~Jehr\in2ls Conneced
~h Swi ches “
USHT % !?
Three termina s are ocated direct y above
_ each re ay on the computer pane . These
OO o O \ . . 7 i i i i
H J termina s are connected under the pane to
the re ay co i . Two termina s are connected
A . direct y to the re ay co i , and the third
OO J termina is connected to a ight wired in
t- N / series with the re ay coi as shown.
—— When the re ay coi is energized
by connecting power to C and F,
the ight direct y be ow the re ay comes
ON because the ight is wired in series
with the re ay co i . If the re ay coi is
energized by supp ying power through contacts
E and F, the ight beneath the re ay wi NOT
come on because there is no current f owing through
the ight. The ight be ow the re ay coi may be used to
show when the re ay is O N .
The circuit drawing for a re ay switch ooks ike this: m*00
The fo owing experiments demonstrate re ay operation
with pushbuttons and ights in simp e computer circuits Rfi-tay Swi ches A w aYS
operate together

EXPERIMENT
0
^This experiment demonstrates the basic e ectrica
operation of a re ay. Additions to the "manua
| re ay operation" circuit of Experiment 6 permit
- I the re ay to be operated e ectrica y
through a pushbutton.
ELECTRICAL RELAY OPERATION
2)
3 )
4)
The program for connecting the switch
contacts of re ay 1 as shown in
Experiment 6 is: 1+/1H 1G/1A
1J/2A 2B/2-
1B/1-
The program for connecting the coi of
re ay 1 through the norma y open
contact of pushbutton 1 is: 1+/1Y
1X/1E
Turn power O N . Light 2 comes O N .
1F/1-
Press down pushbutton 1 and see the
re ay operate. The re ay makes a "c ick"
as the coi is energized, and the re ay contacts
switch the ights. Light 2 goes OFF and
ight 1 comes O N . Operate the re ay severa times
with pushbutton 1 and watch the movement of
the re ay contacts.
ght
5J Now, connect the other set of re ay contacts
(1 K, 1L, IN ) to two unused ights so one ij
comes ON when the re ay is OFF and the
other ight comes ON when the re ay is
O N . Try this yourse f.
£^To modify this program so that the coi indicator
amp wi ight when the coi of re ay 1 is
energized: remove connection 1)^/1 E
add connection D y C
The circuit for this modified part of the program is:
12
1+ iy
—•- IX 1C
0
IE IF
9 00000 f I- The dotted ine in this circuit indicates that
contacts 1G , 1 H, and 1J are part of the re ay
switch contro ed by the coi connected
between IE and IF .
PLATE The re ay is made with a sma e ectro-magnet co i . When current f ows through
the co i , a magnetic force is produced which pu s on the sma meta p ate attached
to the p astic crossbar to switch the contacts. In this experiment, we have seen the
operation of the e ectro-magnet and have operated the re ay to contro a set of ights.
We have a so seen the re ay indicator amp ight when the re ay was turned O N .

EXPERIMENT 8
RELAY CONTROLS ANOTHER
■ his experiment shows how a re ay may be used to
contro another re ay.
| ) The program for this circuit is:
14-/1V 1+/1H 2+/2H
1 V 1C 1G/2C 2G/2A
1 F/ - 2F/2- 2B/2-
2*3 Turn power ON and manua y
operate re ay 2 by pushing the
p astic crossbar to the eft.
See ight 2 come O N .
31 Re ease re ay 2 and manua y
operate re ay 1 . As you push
on the p astic crossbar
of re ay 1, re ay 2 wi c ick ON
AND LIGHT 2 WILL COME O N .
The switch contacts of re ay J_
supp y power to re ay 2 by c osing
the circuit to the coi of re ay 2_.
Re ease re ay 1 and press pushbutton 1 .
Re ay 1 is turned ON by pushbutton 1,
re ay 2 is turned ON by the switch
contacts of re ay 1, and ight 2 is turned
ON by the switch contacts of
re ay 2. Thus, the pushbutton
contro s re ay 2 through the
contacts of re ay 1.
5>1 It is possib e to connect severa
re ays in a series, where each re ay
contro s another. Expand the
present circuit to use a six re ays
with each re ay contro ing the
coi of the next. The ast re ay
in the series, re ay 6, shou d
turn ight 6 ON .
The circuit ooks ike this:
2 J
2+. 2H i 23 2A

EXPERIMENT — I
IJ The program for this circuit is:
J IF / 1- 2Y /2+
1 C/1 X 2Z/1L
1Y/2Y 1K/1C
A RELAY CONTROLS ITSELF
I his experiment demonstrates how a re ay
may be used to contro its own operation.
The re ay is connected to remain ON when it
is turned O N , and to remain OFF when it is
turned O FF. The re ay remains in one of the
two conditions (ON or OFF) unti signa ed
by one of the pushbuttons to change to the
Push pushbutton 1 and re ease. The
re ay indicator ight comes ON and stays
O N . The re ay stays ON because an e ectric
circuit is comp eted through its own contacts
to energize the co i .
Push pushbutton 2 and re ease. This
momentari y interrupts current f ow
through the coi and turns the re ay O FF.
The re ay indicator ight turns OFF and
shows that the re ay is no onger energized.
The re ay circuit has now returned to its
origina condition.
Operate the circuit back and forth ^ '
a few times by first pushing push
button 1; then pushbutton 2.
The circuit used in this experiment is ca ed
"bistab e" because it is ab e to remain in
either of two stab e conditions. Many
different types of "bistab e" circuits are
used in modern digita computers. t +
The two stab e conditions of the re ay circuit
(ON and OFF) are used by the computer in ater
experiments to represent two numbers. When the
re ay is O FF, the number zero (0) is represented.
When the re ay is O N , the number one (1) is
represented. The re ay circuit thus remembers
(stores) these binary numbers.
r
IN
2X
1Z
iy IX 1C 0000 0
1£ IF I-
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17

r
SLIDE SWITCHES
$ i x identica s ide switches abe ed "Secondary
Storage" are used by M INIVAC 601 for manua
storage of data and for other computer switching
functions. Each switch has two sets of contacts
which open and c ose together.
The s ide switch is set to one of two positions by the computer
operator, and it stays in that position unti moved. The
switch thus "remembers" its position and "stores" this
information. The s ide switch a so provides a convenient
means for changing circuits which are programmed
on the computer, and it may be used for
other computer switching functions as we .
Each of the six s ide switches has six termina s
A O 0®ocated direct y above it on the computer
pane . These termina s are connected
underneath the pane to the
s ide switch contacts. The
termina s are abe ed
R ,S ,T , U ,V , W, and
are connected in the same
manner for a six switches.
Each switch is identified
by its section number.
4 » *
When the switch is pushed to the eft,
separate e ectrica connections are made
between termina s S and R and between
termina s V and U:
When the switch is pushed to the right,
separate e ectrica connections are made
between termina s S and T and between
termina s V and W:
18
R S V w R S T W