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is useful since the B-H relationship is extremely nonlinear and irreversible.
For example,
if a core is initially in state 0, as magnetizing force is increased, B is slightly affected
until H approaches H
1
.
As H increases from H
1
to Hz, total flux reversal occurs (path a).
At Hz, the core may be considered saturated in the opposite state such that an additional
increase in H cannot significantly alter B.
Irreversibility is shown by the fact that, as H is
relaxed from Hz to 0, B returns to state 1 rather than starting point 0.
However, state 0
can again be realized by applying sufficient Hof opposite polarity to traverse path b.
B=O
211
l •
I· .
1
H=O
H
-
Hz
Figure Z-Z5.
Typical B-H Characteristics
The threshold characteristic of the device allows its use in a coincident-current
selection scheme such as thatshowninFigure 2-26.
Each core in the array is linked by an
X- and Y - drive line.
Subscripts Rand W refer to read and write and+ and - are polarity
(direction) indicators.
The current magnitude of IY or IXR corresponds to H
1
, or less, and
their sum corresponds to a field exceeding HZ.
Currents of this magnitude entering a core
from the same side will produce a field exceeding Hz.
Currents entering from opposite
sides will have mutually cancelling fields resulting in H
=
0.
Currents IXR and IXW have
the same amplitude but opposite polarity as do IY + and IY -.
Each X- and Y- drive line links two cores in one bit array.
The X- drive line is
common to all bits.
However, each bit has its own Y - drive lines.
Prefixes 01 and 05 on
the drive lines correspond to bits 1 and 5, respectively.
Bits 1 and 5 are used in this ex-
ample because they are physically located in the top and second planes in 4K and 8K memories.
If one X- drive line and one Y- drive line are energized, only one core in the en-
tire array will see a magnetic field strong enough to cause it to change state.
For example,
if Xl and 01 Yl are energized with IXR and IY +, core C
1
11+ will be switched to the clock-
wise magnetic state (if not already in that state).
C
1
11- is subjected to a net field of zero
2-34
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