© 1993 Microchip Technology Inc.

DS00540B-page 7

Implementing IIR Digital Filters

4

;

;

This time is less than 2 Khz (500 uSec),

;

which means real time filtering is possible

;

;*******************************************************************

;*******************************************************************

;

;

CBLOCK

0

0000 0004

B0,B1,B2,B3

ENDC

;*******************************************************************

;

CBLOCK

0x18

0018 0004

DPX,DPX1,DPX2,DPX3

; arithmetic accumulator

001C 0004

AARG,AARG1,BARG,BARG1

; multiply arguments

ENDC

;

CBLOCK

0020 0002

Dn1, Dn1_Hi

0022 0002

Dn1_1, Dn1_1_Hi

0024 0002

Dn1_2, Dn1_2_Hi

0026 0000

0026 0002

Dn2, Dn2_Hi

0028 0002

Dn2_1, Dn2_1_Hi

002A 0002

Dn2_2, Dn2_2_Hi

ENDC

CBLOCK

002C 0002

A11, A11_Hi

002E 0002

A12, A12_Hi

0030 0002

B10, B10_Hi

0032 0002

B11, B11_Hi

; 1st Section Filter Co-efficients

0034 0002

B12, B12_Hi

0036 0000

0036 0002

A21, A21_Hi

0038 0002

A22, A22_Hi

003A 0002

B20, B20_Hi

003C 0002

B21, B21_Hi

; 2nd Section Filter Co-efficients

003E 0002

B22, B22_Hi

ENDC

CBLOCK

0040 0002

X, X1

; 16 bits of input stream

0042 0002

Y, Y1

; 16 bits of filter output

0044 0000

0044 0004

ACC, ACC1, ACC2, ACC3

; 32 bit accumulator for computations

ENDC

;

0002

FltStage

.set

2

000A

NumCoeff

equ

(5*FltStage) ; 5 Co-eff per stage

;

0001

LPASS

.set

TRUE

0000

HPASS

.set

FALSE

0000

BPASS

.set

FALSE

; select the desired filter type

0000

BSTOP

.set

FALSE

;

0001

SIGNED

equ

TRUE

; Set This To ‘TRUE’ for signed multi

;

; and ‘FALSE’ for unsigned.

;

;*******************************************************************

;

Test Program For Low Pass Filter

;*******************************************************************

ORG

0x0000

;

start

0000 E00D

call

initFilter

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