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Converting IF Statements to Differential Current Switch SELECT Functions

IP.com Disclosure Number: IPCOM000035751D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Weinberger, A: AUTHOR

Abstract

Fig. 1 shows a sequential set of IF statements in flow chart form to be implemented in logic. Normally, the logic is implemented from top to bottom, i.e., G1.D1+G1.G2.D2+G1. .... G(N-1).GN.DN+G1. .... GN.D(N+1). Instead, the sequence of IF statements is directly mapped into a corresponding sequence of 2-way SELECT functions with a bottom to top flow of logic, as shown in Fig. 2.

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Converting IF Statements to Differential Current Switch SELECT Functions

Fig. 1 shows a sequential set of IF statements in flow chart form to be implemented in logic. Normally, the logic is implemented from top to bottom, i.e., G1.D1+G1.G2.D2+G1. .... G(N-1).GN.DN+G1. .... GN.D(N+1). Instead, the
sequence of IF statements is directly mapped into a corresponding sequence of 2-way SELECT functions with a bottom to top flow of logic, as shown in Fig. 2.

A differential current switch (DCS) circuit that can implement a 2-way SELECT function as a single logic gate, in addition to implementing a 2-way XOR, OR, and AND, is described in [*]. Also described are DCS dotting functions, AND-dot, OR-dot, XOR-dot and SELECT-dot.

Using the referenced DCS logic symbols, Fig. 3 shows a sequential set of 15 2-way SELECT functions, deserialized in Fig. 4 into a 2-stage tree of 4-way SELECT functions.

(Image Omitted)

The function F represents, for example, the condition that a 16-bit positive integer D (D1,...,D16 - high to low order) is greater than a 16-bit positive integer E, according to the equation below. (D greater than E) =G1.D1 G1.G2.D2

G1. ... .G14.G15.D15

G1. ... .G14.G15.D16
=G1.D1+G1.(G2.D2+...+G14.(G15.D15+G15.D16). ...)
where G1 = Di xor Ei and Gi.Di = (Di xor Ei).Di = Di.Ei.

Replacing Di with its complement in Figs. 3 and 4 produces the function, D less than E.

More generally, any tree of IF statements directly maps into a corresponding tree of 2-way SELECT functions, as...