Electrical pulse counters – pulse dividers – or shift registers: c – Shift register – Shift direction control
Patent
1996-09-10
1998-08-04
Wambach, Margaret Rose
Electrical pulse counters, pulse dividers, or shift registers: c
Shift register
Shift direction control
377 81, G11C 1900
Patent
active
057906262
ABSTRACT:
A unified bi-directional LFSR is fabricated from latches having dual (Forward and Reverse) inputs. Each such latch accepts its inputs upon receipt of a clock signal that is respectively associated with the forward or reverse direction. The appropriate collection of XOR gates exists between latch outputs and the inputs associated with a forward clock signal, so as to produce the forward sequence. Likewise, another appropriate collection of XOR gates exists between the latch outputs and the inputs associated with the reverse clock signal. To produce a "reverse" LFSR corresponding to the polynomial that is the reciprocal of the polynomial for the "forward" LFSR, the latches of the reciprocal (reverse direction) LFSR are construed as being numbered in the opposite order. That is, a single set of latches (register) has both a forward linear feedback network and a reverse linear feedback network. Only one of these two feedback networks is used at a time, but they can intermix forward and reverse steps and appear to index back and forth along the native sequence of the LFSR. That is, steps in reverse undo the most recent forward steps, and vice versa. The bi-directional LFSR is also equipped with a way to preset the latches to a preselected initial value, and it is compatible with the production of all zeros. This last feature latches for a desired n-many bit word! and using it as a valid bit to qualify as correct the remaining latches in the register.
REFERENCES:
patent: 5282234 (1994-01-01), Murayama et al
IBM Tech Disc Bul vol. 27 No. 10A pp. 5718-5720"Ring shifter with externally selectable Modulus "Mar. 1985.
Dixon Daniel J.
Johnson David J.
Hewlett--Packard Company
Miller Edward L.
Wambach Margaret Rose
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