DEVICES INCORPORATED

Special Arithmetic Functions

08/16/2000LDS.33-O

LSH33

32-bit Barrel Shifter with Registers

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

plexed to 16 Lines

u Full 0-31 Position Barrel Shift

Capability

u Integral Priority Encoder for 32-bit

Floating Point Normalization

u Sign-Magnitude or Two's Comple-

ment Mantissa Representation

u 32-bit Linear Shifts with Sign or

Zero Fill

u Independent Priority Encoder

Outputs for Block Floating Point

68-pin PLCC, J-Lead

FEATURES

DESCRIPTION

LSH33

32-bit Barrel Shifter with Registers

DEVICES INCORPORATED

LSH33 B

LOCK

IAGRAM

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 00000

results in no shift of the

input field. A code of 00001

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 11111

) 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.

MS/LS

32-bit

BARREL

SHIFT

ARRAY

2:1

32:5

PRIORITY

ENCODE

SIGN

NORM

RIGHT/LEFT

FILL/WRAP

2:1

ENO

CLK

ENI

CLK

FTO

FTI

2:1

-I

-Y

SI/O

-SI/O

08/16/2000LDS.33-O

Special Arithmetic Functions

DEVICES INCORPORATED

LSH33

32-bit Barrel Shifter with Registers

ABLE

RAP

ODE

HIFT

ODE

EFINITIONS

Shift Code

· · ·

00000

· · ·

00001

· · ·

00010

· · ·

00011

· · ·

01111

· · ·

10000

· · ·

10001

· · ·

10010

· · ·

11100

· · ·

11101

· · ·

11110

· · ·

11111

· · ·

ABLE

ILL

ODE

HIFT

ODE

EFINITIONS

-- L

EFT

HIFT

In fill mode, as in wrap mode, the shift
code input represents the number of
shift positions directly for left shifts,
but the two's complement of the shift
code results in the equivalent right
shift. However, for fill mode the R/L
input can be viewed as the most
significant bit of a 6-bit two's comple-
ment shift code, comprised of R/L
concatenated with the SI

lines.

Thus, a positive shift code (R/L = 0)
results in a left shift of 031 positions,
and a negative code (R/L = 1) a right
shift of up to 32 positions. The LSH33
can thus effectively select any contigu-
ous 32-bit field out of a (sign extended
and zero filled) 96-bit "input."

OUTPUT MULTIPLEXER

The shift array outputs can be regis-
tered and then applied to a 2:1 multi-
plexer controlled by the MS/LS select
line. This multiplexer makes available
at the output pins either the most
significant or least significant 16
outputs of the shift array.

PRIORITY ENCODER

The 32-bit input bus drives a priority
encoder which is used to determine
the first significant position for
purposes of normalization. The
priority encoder produces a five-bit
code representing the location of the
first non-zero bit in the input word.
Code assignment is such that the
priority encoder output represents the
number of shift positions required to
left align the first non-zero bit of the
input word. Prior to the priority
encoder, the input bits are individu-
ally exclusive OR'ed with the SIGN
input. This allows normalization in
floating point systems using two's
complement mantissa representation.
A negative value in two's complement
representation will cause the exclusive
OR gates to invert the input data to
the encoder. As a result, the leading
significant digit will always be "1."

Shift Code

· · ·

00000

· · ·

00001

· · ·

00010

· · ·

00011

· · ·

01111

· · ·

10000

· · ·

10001

· · ·

10010

· · ·

11100

· · ·

11101

· · ·

11110

· · ·

11111

· · ·

DEVICES INCORPORATED

Special Arithmetic Functions

08/16/2000LDS.33-O

LSH33

32-bit Barrel Shifter with Registers

ABLE

ILL

ODE

HIFT

ODE

EFINITIONS

-- R

IGHT

HIFT

ABLE

RIORITY

NCODER

UNCTION

ABLE

· · ·

Shift Code

· · ·

00000

· · ·

00001

· · ·

00010

· · ·

01111

· · ·

10000

· · ·

10001

· · ·

11110

· · ·

11111

· · ·

11111

This affects only the encoder inputs;
the shift array always operates on the
raw input data. The priority encoder
function table is shown in Table 4.

NORMALIZE MULTIPLEXER

The NORM input, when asserted,
results in the priority encoder output
driving the internal shift code inputs
directly. When using the NORM
function, the LSH33 should be placed
in fill mode, with the R/L input low.

When NORM is high (not asserted),
the SI/O

SI/O

port acts as the shift

code input to the shifter.

APPLICATIONS EXAMPLES

Normalization of mantissas up to 32
bits can be accomplished directly by a
single LSH33. To do this, the NORM
input is asserted, and fill mode and
left shift are selected. The normalized
mantissa is then available at the
device output in two 16-bit segments,
under the control of the output data
multiplexer select, the MS/LS signal.

If it is desirable to avoid the necessity
of multiplexing output data in 16-bit
segments, two LSH33 devices can be
used in parallel. Both devices receive
the same input word, with the MS/LS
select line of one wired high, and the
other low. Each device will then
independently determine the shift
distance required for normalization,
and the full 32 bits of output data will
be available simultaneously.

Shift Code

· · ·

00000

· · ·

00001

· · ·

00010

· · ·

00011

· · ·

01111

· · ·

10000

· · ·

10001

· · ·

10010

· · ·

11100

· · ·

11101

· · ·

11110

· · ·

11111

· · ·

08/16/2000LDS.33-O

Special Arithmetic Functions

DEVICES INCORPORATED

LSH33

32-bit Barrel Shifter with Registers

Symbol

Parameter

Test Condition

Min

Typ

Max

Unit

Output High Voltage

= Min., I

= 2.0 mA

2.4

Output Low Voltage

= Min., I

= 8.0 mA

0.4

Input High Voltage

2.0

Input Low Voltage

(Note 3)

0.0

0.8

Input Current

Ground

(Note 12)

µA

Output Leakage Current

Ground

OUT

(Note 12)

µA

CC1

Current, Dynamic

(Notes 5, 6)

CC2

Current, Quiescent

(Note 7)

1.5

Storage temperature ........................................................................................................... 65°C to +150°C

Operating ambient temperature ........................................................................................... 55°C to +125°C

supply voltage with respect to ground ............................................................................ 0.5 V to +7.0 V

Input signal with respect to ground ........................................................................................ 3.0 V to +7.0 V

Signal applied to high impedance output ............................................................................... 3.0 V to +7.0 V

Output current into low outputs ............................................................................................................. 25 mA

Latchup current ............................................................................................................................... > 400 mA

AXIMUM

ATINGS

Above which useful life may be impaired (Notes 1, 2, 3, 8)

PERATING

ONDITIONS

To meet specified electrical and switching characteristics

LECTRICAL

HARACTERISTICS

Over Operating Conditions (Note 4)

Mode

Temperature Range (Ambient)

Supply

Voltage

Active Operation, Commercial

0°C to +70°C

4.75 V

5.25 V

Active Operation, Military

55°C to +125°C

4.50 V

5.50 V

DEVICES INCORPORATED

Special Arithmetic Functions

08/16/2000LDS.33-O

LSH33

32-bit Barrel Shifter with Registers

1234567890123

123456789012345678901234567

LSH33-40*

-Y

-SO

SWITCHING CHARACTERISTICS -- C

OMMERCIAL

PERATING

ANGE

(0°C to +70°C)

UARANTEED

AXIMUM

OMBINATIONAL

ELAYS

Notes 9, 10 (ns)

To Output

From Input

FTI = 0, FTO = 0

CLK

MS/LS

FTI = 0, FTO= 1

CLK (NORM = 0/1)

-SI

R/L, F/W

MS/LS

FTI = 1, FTO = 0

CLK

MS/LS

FTI = 1, FTO = 1

-I

, SIGN

(NORM = 0/1)

-SI

R/L, F/W

MS/LS

LSH33-30

-Y

-SO

LSH33-20*

-Y

-SO

Input

-I

, SIGN

-SI

R/L, F/W

ENI, ENO

UARANTEED

INIMUM

ETUP

AND

OLD

IMES

ITH

ESPECT

LOCK

ISING

DGE

Notes 9, 10 (ns)

LSH33-30

FTI = 0

FTI = 1

Setup Hold

LSH33-20*

FTI = 0

FTI = 1

Setup Hold

LSH33-40*

FTI = 0

FTI = 1

Setup Hold

-S

TATE

NABLE

ISABLE

IMES

Notes 9, 10, 11 (ns)

LSH33-40*

LSH33-30

LSH33-20*

ENA

DIS

LOCK

YCLE

IME

AND

ULSE

IDTH

Notes 9, 10 (ns)

Minimum Cycle Time

Highgoing Pulse

Lowgoing Pulse

LSH33-40*

LSH33-30

LSH33-20*

123456789012345678901234

ISCONTINUED

PEED

RADE

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ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LSH33JC30