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Limited Arithmetic Capability Using a Single Register

IP.com Disclosure Number: IPCOM000075185D
Original Publication Date: 1971-Aug-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Larsen, LD: AUTHOR

Abstract

Described is a shift register arrangement providing limited arithmetic capability which may be implemented at very low cost. The illustrated circuit, for example, may be implemented using approximately six TTL modules and in the form described is appropriate for use in many small processors.

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Limited Arithmetic Capability Using a Single Register

Described is a shift register arrangement providing limited arithmetic capability which may be implemented at very low cost. The illustrated circuit, for example, may be implemented using approximately six TTL modules and in the form described is appropriate for use in many small processors.

The circuit utilizes a shift register having, for example, eight positions with a parallel input and a feedback loop from the last position of the shift register through an AND circuit, a selective inverter, a (+1) adder element and a second selective inverter back to the first position of the shift register. Each of the circuits in the feedback path include a control input, which is under control of one position of a four-bit control signal. A second shift register control is arranged to receive a count-control signal which controls the number of shifts executed in the shift register. When the count reaches zero or some other predetermined value, shifting of the data inserted in parallel into the shift register is stopped and the desired result resides in the shift register and may be read in parallel.

The four feedback elements controlled by the four-bit control signal operate as follows.

The AND gate output will always be zero if the control input is zero. However, if the control input is one, the AND gate output will be the same as the input from the last position of the shift register.

Both selective inverters will pr...