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Figure 2-42.
Coincident Current
Addressing
Core Storage· Addressing
+
•
Transistors select address and pro-
vide selection current.
•
Current flow in drive line deter-
mines core magnetic polarity.
It is possible to apply the 2-wire.
2-30
coincident-current addressing scheme to
a larger number of cores.
In Figure
2-43, magnetic cores have been added to
the 8,192-position, 13-digit storage
addressing scheme explained previously.
Each box represents a magnetic core, and
the lines between the boxes represent
the screen of wires.
If a battery is
connected between the bottom address
selection switch and the top address
selection switch, and if a similar bat-
tery is connected between the left
address selection switch and the right
address selection switch, coincident
current will be produced in
~
core.
That one core will be flipped to a
polarity dependent on the direction of
current flow (Figure 2-44).
The core
shown can be flipped to the opposite
state by changing the position of the
battery control switch.
The four
address selection switches shown corres-
pond to the address selection switches
in Figure 2-43.
The use of switches for address sel-
ection and polarity control produces the
desired result.
However, having a ser-
ies of switches is awkward.
Moreover,
it is impossible for such a system to be
operated at the speeds required by the
IBM 2030 Processing Unit.
A much more
practical approach is to let transistors
do the switching for address selection.
Figure 2-45 shows the windings through a
typical core, and the method of driving
the windings with sufficient current to
flip the core to a logical
1.
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