| 摘要 |
This adder/subtractor, in which the additions are carried out in normal manner and the subtractions are carried out by means of additive subtraction, exhibits a tetrad adder according to P 3434243.5. The nines complement number of the subtrahend required with additive subtraction is supplied by the dual circuit 5-6 which consists of the recoding circuit 5 and the nines complement circuit 6. The recoding circuit 5, which converts BCD-8421-coded decimal numbers into 1-of-10-coded decimal numbers, is required because direct nines complementing of BCD-8421-coded decimal numbers is not possible. Any carry from the previous addition is processed non-negated in the main circuit 1. Any carry from the previous additive subtraction is processed negated in the main circuit 1. <IMAGE>
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