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Eight Bit Arithmetic and Logic Unit

IP.com Disclosure Number: IPCOM000082684D
Original Publication Date: 1975-Jan-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 5 page(s) / 171K

Publishing Venue

IBM

Related People

Bodner, RE: AUTHOR [+2]

Abstract

An arithmetic and logic unit (ALU) uses four control lines and a mode line to control the functions performed by the ALU.

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Eight Bit Arithmetic and Logic Unit

An arithmetic and logic unit (ALU) uses four control lines and a mode line to control the functions performed by the ALU.

The ALU is shown as having eight bit operand inputs Y8-Y15 and X8-X15. Control lines 0-3, mode and carry in are developed in response to decoding arithmetic or logic instructions and the conditions of a processor condition register, not shown.

The circuits noted by (1) generate the signals -- FUN8 - FUN15 inclusive. The circuits noted by (2) form exclusive OR circuits for +DATA8 - +DATA15 inclusive. The circuits noted by (3) generate both internal and off chip carries. They enable the use of the functions at points labelled A to generate the carries. This eliminates the need to generate special functions, and thus reduces the number of circuits required. The carry out signal is degated during logical operations, see the circuit noted (4).

(Image Omitted)

The functions performed by the ALU and the status of the control and mode lines are shown in Fig. 2.

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