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E L E C T R I C A L
P R I N C I P L E S
59
varying the position of the tap switch, the voltage
across the secondary is changed. Since the voltage
drop across the tube and the choke does not vary
to any extent, any change in the secondary volt-
age will result in a change in the +I50 volt line.
147 to 152 volts are acceptable.
After the + I 50 volt line is adjusted, the bias
voltages may be adjusted in any order. The -100
volt line and the -250 volt line are both adjusted
by means of potentiometers. Both potentiometers
are accessible from athe rear of the power supply
chassis. The +65 volt supply is also adjusted by
means of a potentiometer in the B chassis.
PRINCIPLE OF MULTIPLYING
Multiplication is performed in this machine by
over-and-over addition of the multiplicand factor.
The value of the multiplier digit determines the
number of times that the multiplicand is to be
added into the product counter. The order of the
digit (i.e., units, tens, etc.) determines which posi-
tions of the product counter will receive the mul-
tiplicand factor and also during which column
shift cycle the adding will take place. An example
of multiplication by over-and-over addition is
shown in Figure 58. Observe that no adding oc-
curs in the 12th position of the product counter;
this position is reserved for carry-overs.
This
method of multiplication is the simplest possible
since only three counters are required. This mehod
is not feasible for mechanical machines, because
the time required to complete a problem is too
great.
However, electronic addition is so rapid
that it permits use of rhis simple method. The time
required by the electronic unit to complete a prob-
lem by this method corresponds to slightly over
one-half a cycle point of mechanical movement of
the card through the punch unit.
Observe that the column shifting is performed
in the reverse order to that customarily done when
multiplying by hand. The order of column shift-
ing is immaterial, as the final result will be the
same regardless of rhe order in which the multiplier
factors are taken. In the 603 multiplier, column
.
shifting is from the 6th multiplier position to the
first simply because the earliest engineering model
required it. When changes were made which no
longer required reverse column shihing, it was felt
that it was not feasible to make the necessary cir-
cuit changes to establish normal column shifting.
Note from Figure 58 that no addition occurs
during column shift cycles in which rhe multiplier
is 0. Mechanical machines usually have some ar-
rangement to test for 0's so that all multiplier posi-
tions containing
O
may be slripped. This compli-
cates the machine but saves time.
Where time is
not a factor, this unnecessary complication may be
eliminated by completing all the column shift
cycles regardless of the value of the multiplier
digit. This is done in the 603 electronic comput-
ing unit; six column shift cycles are taken for
every multiplication regardless of the value of the
multiplier.
Also observe from Figure 58 that the multipli-
cand is added into the product counter as many
times as the value of the multiplier digit by which
multiplication is taking place.
This means that
during any given column shift cycle, the multi-
plicand may have to be added as many as 9 times.
Again, to avoid unnecessary complications a fixed
number of adding cycles are taken each column
shift cycle regardless of the value of the multi-
plier digit.
In the 603 compu~ing circuits ten
adding cycles are taken during each column shift
cycle rather than nine for reasons explained later.
This means that each multiplication consists of six
groups of ten adding cycles, or a total of 60 add-
ing cycles.
The computing section of the 603 multiplier is
arranged so that a definite number of voltage
pulses represent an adding cycle. For an analogy
to a mechanical machine, one pulse may be con-
sidered as one cycle point of the basic adding cycle.
The basic adding cycle consists of 16 pulses; 10 are
reserved for adding, 4 for carrying, and the other
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