LSH33 datasheet(1/8 Pages) LODEV

部件名	LSH33

功能描述	32-bit Barrel Shifter with Registers

PDF	8 Pages

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制造商	LODEV [LOGIC Devices Incorporated]

网页	http://www.logicdevices.com

标志

1 / 8 page

DEVICES INCORPORATED

Special Arithmetic Functions

08/16/2000–LDS.33-O

1

LSH33

32-bit Barrel Shifter with Registers

u

u 32-bit Input, 32-bit Output Multi-

plexed to 16 Lines

u

u Full 0-31 Position Barrel Shift

Capability

u

u Integral Priority Encoder for 32-bit

Floating Point Normalization

u

u Sign-Magnitude or Two’s Comple-

ment Mantissa Representation

u

u 32-bit Linear Shifts with Sign or

Zero Fill

u

u Independent Priority Encoder

Outputs for Block Floating Point

u

u 68-pin PLCC, J-Lead

FEATURES

DESCRIPTION

LSH33

32-bit Barrel Shifter with Registers

DEVICES INCORPORATED

LSH33 BLOCK DIAGRAM

The LSH33 is a 32-bit high speed

shifter designed for use in floating

point normalization, word pack/

unpack, field extraction, and similar

applications. It has 32 data inputs,

and 16 output lines. Any shift con-

figuration of the 32 inputs, including

circular (barrel) shifting, left shifts

with zero fill, and right shifts with

sign extension are possible. In addi-

tion, a built-in priority encoder is

provided to aid floating point normal-

ization.

Input/Output registers provide

complete pipelined operation. Both

have independent bypass paths for

complete flexibility. When FTI = 1,

the input registers are bypassed.

Likewise, when FTO= 1, the output

registers are bypassed.

SHIFT ARRAY

The 32 inputs, which can be regis-

tered, to the LSH33 are applied to a

32-bit shift array. The 32 outputs,

which can also be registered, of this

array are then multiplexed down to

16 lines for presentation at the device

outputs. The array may be configured

such that any contiguous 16-bit field

(including wraparound of the 32

inputs) may be presented to the

output pins under control of the shift

code field (wrap mode). Alterna-

tively, the wrap feature may be

disabled, resulting in zero or sign bit

fill, as appropriate (fill mode). The

shift code control assignments and the

resulting input to output mapping for

the wrap mode are shown in Table 1.

Essentially the LSH33 is configured as

a left shift device. That is, a shift code

of 000002 results in no shift of the

input field. A code of 000012 provides

an effective left shift of 1 position, etc.

When viewed as a right shift, the shift

code corresponds to the two’s comple-

ment of the shift distance, i.e., a shift

code of 111112 (–110) results in a right

shift of one position, etc.

When not in the wrap mode, the

LSH33 fills bit positions for which

there is no corresponding input bit.

The fill value and the positions filled

depend on the RIGHT/LEFT (R/L)

direction pin. This pin is a don’t care

input when in wrap mode. For left

shifts in fill mode, lower bits are filled

with zero as shown in Table 2. For

right shifts, however, the SIGN input

is used as the fill value. Table 3

depicts the bits to be filled as a

function of shift code for the right shift

case. Note that the R/L input changes

only the fill convention, and does not

affect the definition of the shift code.

16

OE

MS/LS

32-bit

BARREL

SHIFT

ARRAY

16

2:1

32:5

PRIORITY

ENCODE

32

5

32

SIGN

NORM

RIGHT/LEFT

FILL/WRAP

5

GG

2:1

ENO

CLK

ENI

CLK

FTO

FTI

G

2:1

5

I31-I0

Y15-Y0

SI/O4-SI/O0

16

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