Electronic digital logic circuitry – Multifunctional or programmable – Array
Patent
1992-08-27
1995-07-11
Westin, Edward P.
Electronic digital logic circuitry
Multifunctional or programmable
Array
326 38, H03K 19173, G06F 738
Patent
active
054323886
ABSTRACT:
A typical Programmable Logic Array (PLA) provides an available logic function, or precursor, which a user modifies to obtain a desired logic function. For example, the precursor may be (A.multidot.A19 B.multidot.B+(A.multidot.A.multidot.B.multidot.B). The user obtains the desired function, such as (A.multidot.)+(A.multidot.B), by blowing fuses inside the PLA. The fuse-blowing physically blocks data signals (such as the deleted and the deleted B in the first term) from reaching an internal AND gate which performs the ".multidot." operation. However, this fuse-blowing is permanent, and irreversible. In contrast, one form of the invention does the blocking by using a NAND gate. That is, the data signal, such as the "B," is applied to one input of the NAND gate. A capacitor is connected to the other input. The user stores either a ONE or a ZERO on the capacitor. A ONE blocks the data signal (the output of the NAND cannot change). A ZERO passes the data signal (the output is the inverse of the data signal). Thus, not only is the PLA PROGRAMMABLE, but is also REPEATEDLY PROGRAMMABLE: the signal on the capacitor can be changed.
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Crafts Harold S.
McKinley William W.
AT&T Global Information Solutions Company
Bailey Wayne P.
Foote Douglas S.
Roseen Richard
Welte Gregory A.
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