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Address
Selection
and Drive
Figure 2-49.
Core Plane Stacking
•
•
Nine core planes wired together to
provide nine cores for each address.
Coincident current produced in nine
core windings.
Up to this point, we have been speaking
of a single core plane consisting of
8,192 cores.
This plane can store 8,192
bits of information.
At any time, by
correctly impulsing the proper drive
line, a single bit of information can be
stored or retrieved.
In the IEM 2030,
it is necessary to store a whole byte of
information at each storage location.
Each byte consists of eight information
bits plus a parity bit.
To store a
complete byte requires nine cores (eight
informaion cores plus a parity core) •
In Figure 2-49, nine 8, 192-core planes
have been stacked, and the address lines
have been tied together serially.
If
two address lines are selected and are
driven with coincident current, nine
cores are affected.
(one in each core
plane), because coincident current is
produced in the same relative core in
each of the nine identical core planes.
Inhibit
•
Controls writing in cores.
2-38
•
•
Address
Selection
and Drive
Sense winding shared by inhibit
circuits.
Inhibit current prevents core from
setting.
•
Inhibit current opposes X-drive
current.
The 8, 192-position core storage unit
shown in Figure 2-49 has a deficiency:
it can store only all bits or no bits in
a given storage location.
To make the
core-storage unit useful, we must be
able to write in cnly the desired cores
within a given core-storage location.
This is necessary because a core-
storage position containing useful
information has some cores set to logi-
cal 1 and some cores set to logical O.
Additional control over the writing of
the cores is provided
by
the principle
known as inhibiting.
In Figure 2-46, we
added a third wire to the core and used
this wire to sense when the core
flipped.
We can now use this same wire
to control writing in the core.
This
control is accomplished by sending cur-
rent through the third wire during the
time when writing is to take place
(Figure 2-50).
Called inhibit current,
this current is equal to the drive cur-
rent in the X-drive line, but is oppo-
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