Electronic digital logic circuitry – Multifunctional or programmable – Array
Utility Patent
1999-01-27
2001-01-02
Tokar, Michael (Department: 2819)
Electronic digital logic circuitry
Multifunctional or programmable
Array
C326S041000, C326S046000
Utility Patent
active
06169417
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to programmable logic devices, and more particularly product term (“p-term”) macrocells for programmable logic devices.
Pederson U.S. Pat. No. 5,121,006 (“the '006 patent”) shows a p-term-based macrocell for use in programmable logic devices. The '006 patent macrocell is capable of providing the logical OR of N p-terms. In the '006 patent N is up to five, but N can be any number smaller or larger than five as desired. Also in he '006 patent the sum-of-products output of the above-mentioned logical OR can be optionally subjected logical EXCLUSIVE OR combination with any one of the following signals: (1) a p-term, (2) a feedback output (“Q”) from a register in the macrocell, (3) the logical inverse (“Q-bar”) of the just-mentioned feedback, (4) fixed logic 1 potential (“VCC”), or (5) fixed logic 0 potential (“GND”). The ability to select one of the EXCLUSIVE OR inputs (sometimes referred to herein as the “XOR Control” or “XOR_CTRL” input) from among Q-bar, Q, VCC, or GND allows the '006 patent macrocell to implement D or T flip-flops, and also allows inversion control on the input to the register. However, when the XOR Control input is tied to a product term, the '006 patent macrocell loses the ability to select between the D or T flip-flop. Inversion control on the input to the register is also Lost.
In view of the foregoing, it is an object of this invention to provide improved p-term macrocells for programmable logic devices.
It is a more particular object of this invention to provide p-term macrocells for programmable logic devices which allow both inversion control and D/T flip-flop selection even when a p-term is used as a contributor to the XOR Control input.
SUMMARY OF THE INVENTION
These and other objects of the invention are accomplished in accordance with the principles of the invention by providing a p-term macrocell of the general type shown in the '006 patent but with modification of circuitry for providing the XOR Control input. A preferred embodiment of the XOR Control input circuitry of this invention includes NAND circuitry configured to provide the logical NAND of Q and the output signal of a first programmable function control element (“FCE”). This embodiment further includes first EXCLUSIVE OR circuitry configured to provide the logical EXCLUSIVE OR of the output signal of the above mentioned NAND circuitry and the output signal of a second FCE. The embodiment being described still further includes second EXCLUSIVE OR circuitry configured to provide the logical EXCLUSIVE OR of the output signal of the first EXCLUSIVE OR circuitry and a signal which is selectable (typically programmably selectable) as either a p-term or GND. The output signal of the second EXCLUSIVE OR circuitry is the XOR Control signal.
If desired, the modified XOR Control input circuitry of this invention can be implemented using a number of transistors which is only slightly greater than the number of transistors needed for the '006 patent XOR Control input circuitry.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments
REFERENCES:
patent: 5121006 (1992-06-01), Pedersen
patent: 5220214 (1993-06-01), Pedersen
patent: 5821774 (1998-10-01), Veytsman et al.
patent: 5969539 (1999-10-01), Veytsman et al.
patent: 5986465 (1999-11-01), Mendel
patent: 6034540 (2000-03-01), Mendel
Altera Corporation
Chang Daniel D.
Fish & Neave
Jackson Robert R.
Tokar Michael
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