LF48908 datasheet(4/16 Pages) LODEV

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DEVICES INCORPORATED

LF48908

Two Dimensional Convolver

Video Imaging Products

08/9/2000–LDS.48908-J

The filtered image data is output on

the Data Output bus (DOUT19-0). This

bus is registered with three-state

drivers to facilatate use on a standard

microprocessor system bus.

Data Input

Image data is input to the 3 x 3

convolver using DIN7-0. Data present

on DIN7-0 is latched into a program-

mable pipeline delay on the rising

edge of CLK. The programmable

pipeline delay (1 to 4 clock cycles)

allows for synchronization of input

data when multiple LF48908s are

cascaded together to perform larger

convolutions. This delay is pro-

gramed via the Initialization Register

(see Table 3). The image data format,

unsigned or two’s complement, is also

controlled by this register.

Coefficient data is input to the 3 x 3

convolver using either of two Coef-

ficient Registers (CREG0 or CREG1).

The Coefficient Registers are loaded

through CIN7-0 using the A2-0, CS, and

LD controls. The coefficient data

format, unsigned or two’s comple-

ment, is determined by the Initializa-

tion Register.

Arithmetic Logic Unit

The input data path ALU with shifter

allows pixel point operations to be

performed on the incoming image.

These operations include arithmetic

functions, logical masking, and left/

right shifts. The 10-bit ALU Micro-

code Register controls the various

operations. The three upper bits

control the shift amount and direction

while the seven lower bits determine

the arithmetic or logical operation.

The shift operation is performed on

the output of the ALU. This shift

operation is independent of the

arithmetic or logical operation of the

ALU.

Tables 1 and 2 show the operations of

the ALU Microcode Register. The “A”

operand comes from the DIN input

data path, while the “B” operand is

taken from the ALU Register. The

ALU Register is loaded using CIN7-0

and EALU. With EALU HIGH, data

from CIN7-0 is loaded into the ALU

With EALU LOW, the data is held in

the ALU Register. Since CIN7-0 is also

used to load the Control Logic Regis-

ters, it is possible to overwrite data in

those registers if CS and LD are active

when loading the ALU Register.

Therefore, special care must be taken

to ensure that CS and LD are not

active when writing to the ALU

Programmable Row Buffers

The two internal row buffers provide

the delay needed to perform the two-

dimensional convolution. The row

buffers function like 8-bit serial shift

registers with a user-programmable

delay from 1 to 1024 stages (it is

possible to select delay stages of 1 or

2, but this leads to meaningless results

for a 3 x 3 kernel convolution). The

row buffer length is set via the Row

Length Register (see Row Length

connected in series to provide the

proper pixel information to the

multiplier array. The Cascade Output

(CASO7-0) provides a 2X row delay of

the input data allowing for cascading

of LF48908s to handle larger frames

and/or kernel sizes. If more than 1024

delay stages are needed, it is possible

to use external row buffers and bypass

the internal row buffers. Bit 0 of the

Initialization Register determines if

internal or external row buffers are

used. If Bit 0 is a “0”, the internal row

buffers are used. If Bit 0 is a “1”, the

internal row buffers are bypassed and

external row buffers may be used.

3 x 3 Multiplier Array

The multiplier array comprises nine

8 x 8-bit multipliers. The active

Coefficient Register supplies the

coefficents to each of the multipliers,

while the pixel data comes from the

data input path and row buffers. The

array forms a sum-of-products result

as defined by the equation listed in

Figure 3.

CONTROL LOGIC

Four sets of registers, the ALU Micro-

code, Row Length, Initialization, and

Coefficient, define the Control Logic

section. These registers are updated

FIGURE 3.

MULTIPLIER ARRAY OUTPUT

PIXEL INPUT DATA

FILTER KERNEL

MULTIPLIER ARRAY OUTPUT

A(P1)

+ D(P4)

+ G(P7)

B(P2)

E(P5)

H(P8)

C(P3)

F(P6)

I(P9)

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