| 摘要 |
The object of the invention is a tetrad addition and subtraction device in BCD 8421 code, which has: - as the main circuit, a dual tetrad subtractor (1) - as the correction circuit, a subtraction circuit (2) to subtract the number 6 - for carrying out subtractive additions, not a 9s-complement circuit, but a 15s-complement circuit (4), because for BCD 8421 coding a normal negating-complementing circuit is a 15s-complement circuit - also for carrying out subtractive additions, a pre-adder circuit (3) to add the number 6. Thus, in this addition and subtraction device, subtractions are carried out normally, and additions by subtractive addition. For subtraction, the B inputs are the minuend inputs, and the A inputs are the subtrahend inputs. For subtraction, in circuit (4), the complement bypass is pre-triggered, and the pre-adder circuit (3) is not pre-triggered. For subtractive addition, in circuit (4), the complementing is pre-triggered, and the pre-adder circuit (3) is pre-triggered. <IMAGE>
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