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Four Bit Multiply Step using Effective Address Unit

IP.com Disclosure Number: IPCOM000109008D
Original Publication Date: 1992-Jul-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Muhich, JS: AUTHOR

Abstract

Disclosed is a circuit which is used to calculate both an effective address (EA) and 4-bit multiply step. By having a single unit of logic to perform both functions, a substantial savings in silicon area is realized.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 84% of the total text.

Four Bit Multiply Step using Effective Address Unit

       Disclosed is a circuit which is used to calculate both an
effective address (EA) and 4-bit multiply step.  By having a single
unit of logic to perform both functions, a substantial savings in
silicon area is realized.

      The figure on the next page is a data flow diagram of the
combined functional unit.  The effective address calculation require
that a three-way add be performed for the Base, Scaled Index  and the
Displacement as seen in the figure.  The Scaled Index is performed by
the shift mux seen in the figure.  The output of the three-way adder
is the EA Offset address which is later limit checked, clipped, and
added to the base address.  The multiply step function requires a
three-way add along with shifting of the operand much the same as the
Scaled Index operand for the EA calculation.  Also the multiply step
requires the MQ Register to hold the lower 32 bits of the results.
To start the multiply step function the B operand is loaded both into
the B Source Register and the EA Displacement Register.  The A
operand is loaded into the MQ Register.  The A Source Register is
initialized to zero.  Next, 8 steps (clocks) through the logic are
performed accumulating 4 bits of partial product each step until all
32 bits of partial product are collected in the MQ Register.  The MQ
register accumulates 4 bits each step.  After 8 step the Results of
the multiply operation are found as the outpu...