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A method of synthesis of single-level combinatorial circuits with usage of mounting connection of outputs on OR (method M2)

Many PLD have mounting join of external outputs for implementation of the logical function OR. For such join output buffers PLD should be made on the technology with an open collector or to have property of programming of an open-drain (open-drain) for each output. Mounting connection of outputs realizes the function OR in inverse logic. Therefore method M2 is used in digital systems with inverse logic more often. The Essence of method M2 of synthesis of single-level combinatorial circuits(schemes) with join of outputs PLD on OR consists in creation of minimum number T of subsets B1..., BT parts of set functions Y* so that were fulfilled necessary and sufficient conditions of implementation on one PAL (function box CPLD) of all parts of each subset Bt, t =

The last task is reduced to the task of a coating of a Boolean matrix by minors of the limited dimension. In subsequent parts of functions of a part of functions of each subset Bt, t =

are realized on separated PALs. At the final stage of synthesis for each function

i outputs(exits) PAL, on which set Z is realized

(i) Parts of the function

i, i =

, are united with the help mounting OR.
Positive qualities of method M2 are the following:

The combinatorial circuits of the high speed distinguished from single-level circuits considered above only by delay on mounting connection of outputs are created;

Time of creation of various output signals differs a little bit for the period of delay on mounting connection of outputs;

The method allows to apply separate minimization of a Booleen Function System;

Considerably wider area of usage, in comparison with method M1.

The following concerns to disadvantages of method M2:

PLD should be made on the technology with an open collector or to support a programmed option "open-drain";

The method is used in systems with inverse logic;

Inverse representation of functions may be much more complicated than their direct representation.

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