Abstract: A digital arithmetic unit for adding and subtracting multidigit binary coded decimal numbers having a zoned format. Such adding and subtracting is done by means of a parallel binary adder of a type suitable for handling pure binary numbers and having no special provisions for accommodating zoned decimal numbers. The two multidigit zoned decimal numbers to be added or subtracted at any given moment are supplied to the two input sides of such binary adder by way of input modifier circuits which precondition the zone and sign fields in such numbers to enable the proper propagation of digit carries across such zone and sign fields during the performance of the addition inside the binary adder. The resulting binary bit sequence appearing at the output side of the binary adder is passed to an output modifier or corrector which causes the bits in the zone and sign field positions therein to assume the proper zone and sign code values.

Abstract: Data processing circuitry for performing two serially related arithmetic operations during one and the same machine control cycle and employing an independent zone parallel type arithmetic unit capable of simultaneously performing independent arithmetic operations in the different zones thereof. Data transfer circuitry is provided for immediately supplying the output result of a first arithmetic unit zone back to the input of a second arithmetic unit zone for immediately producing a second and different result. Such transfer circuitry is constructed to operate in an asynchronous manner so that the first result is supplied back to the input of the second arithmetic unit zone as soon as it becomes available at the output of the first arithmetic zone. Thus, a second result, which is dependent on the first result, is produced during the same machine control cycle as the first result. This data processing circuitry is particularly useful for providing storage protection for a data processor.

Abstract: A carry look-ahead parallel digital adder having a relatively wide overall data flow width and a pair of automatically adjustable boundary mechanisms for subdividing the adder into plural independent operating zones of variable width and variable location. Anywhere from one to three independent zones may be obtained. Independent external carry-in and carry-out lines are provided for each zone and the connecting points for such lines are automatically shifted in step with the movement of the zone boundaries.

Abstract: A digital arithmetic unit employing a binary adder for adding and subtracting multidigit binary coded decimal numbers in either zoned format or packed format and having an improved method of generating parity check bits for the resultant data bytes produced by the arithmetic unit. When using a binary adder for adding or subtracting binary coded decimal numbers, it is necessary to correct some of the data appearing at the output of the binary adder in order to obtain the correct results. The parity check bit generating circuitry of the present invention, however, works on the uncorrected data appearing at the output of the adder, but nevertheless produces the proper parity check bits for the corrected data which represents the final output for the arithmetic unit. This reduces the amount of time delay which would otherwise be caused by generating the parity check bits in a conventional manner.