Browse Prior Art Database

ARITHMETIC UNIT

IP.com Disclosure Number: IPCOM000022837D
Original Publication Date: 1976-Mar-31
Included in the Prior Art Database: 2004-Mar-27
Document File: 2 page(s) / 325K

Publishing Venue

Xerox Disclosure Journal

Abstract

In a computer Arithmetic Unit, in order to minimize hard-S ware and instruction execution time it is useful to perform various arithmetic functions in different modes. For example, decimal compare is performed efficiently in straight binary, decimal multiply and divide are performed

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Page 1 of 2

XEROX DISCLOSURE JOURNAL

ARITHMETIC UNIT
ProposedMalcolm Thomson Classification

U.s. Cl. 235/156
mt. Cl. G06f 7/38

xx

END

000

00

O~0

~OO 0 O3~

0 0~0 X

0 OO~
0 000 X

x xxx x

M0DIF~ER CONTROL

ROM INPUTS

O III 0 10
0 101
0 100

X SB X SB+6

X SB4~3
x o

(L~.-A)

CONVERT TO EXC~6
CONVERT TOEXC,3

Volume 1 Number 3 March 1976 53

SB +0 SB~6
SB -~3

SB $ 3
58-3

SB

F

A*D~
) ~BCD
AfO)

)

)EXCESS3

  In a computer Arithmetic Unit, in order to minimize hard-S
ware and instruction execution time it is useful to
perform various arithmetic functions in different modes.
For example, decimal compare is performed efficiently in
straight binary, decimal multiply and divide are performed
efficiently in Excess 3 code, and add and substract are
efficiently performed in binary-coded~decimal (BCD) with

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Page 2 of 2

~P.ITHMETIC tTh~IT (Cont~d)

an Excess 6 on one operand

The Decimal PROM 10 of the figure above is a four~-bit
arithmetic unit for implementing Excess 3 and BCD in a
computer ~rithmetic Unit, .Z~ plurality of these devices
may be used for larger words, For example, in a 64~-bit arithmetic Unit, 16 Decimal PROMs may be used, one for
each hexadecimal digit.

additionally, this unit may be used for negating binary
numbers (by inverting ~l) and also provides a source of
zeros and ones (binary).

The data inputs consist of four bits from the Sum Binary
bus (SB) and four input control lines, End Carry (from
the input hex register 12), and three other control lines...