Special carry adder for nine complement carry - delivers false carry when first two digits of serial complement cycle are subtracted additively or vice=versa

摘要

The circuit is necessary only when the dual full adders (5, 6) of a reversible tetrad adder-subtractor are not provided with further adders which render the existing adder (4) superfluous. 16 two-input AND gates (7) are used with 10 two-input and 2 three-input OR gates (8, 9) and four NOT gates (10). A special nine's complement circuit (2) is capacitively coupled (21) to a carry adder (4) based on two simple flip-flops (16, 17) similar to those of the carry storage circuit. USE - In connection with 5211 tetrad adder combined with nine's complement and straight-ahead circuits.