Improved NDRO operation of ferrite cores

A method is reported whereby the useful 1 output of a ferrite core, operated in the NDRO mode based on differential permeability sensing [1], can be increased considerably. The method is particularly suitable for use in program-store applications and in fast word-organized memories. To write, first a clear pulse, then a demagnetizing pulse is applied which is followed by a second demagnetizing pulse of opposite polarity and of short duration. This pulse sequence causes the 1 output to be larger than the largest value that could be achieved by the use of only a single demagnetizing pulse. The second demagnetizing pulse is not related in amplitude to subsequent disturb pulses and, therefore, its amplitude does not have an upper threshold. It is possible to operate in a bit write mode where, having cleared all cores on a givenXline into the 0 state, 1's may be written into any of these cores, one by one or in groups of any number. This mode of operation is attractive for a program store where, while NDRO is necessary, longer write times are acceptable. A worse case output ratio of about 2 to 1 could be achieved on cores that without the application of the second demagnetizing pulse could provide an output ratio of only 1.6 to 1.