Implementing IIR/FIR Filters

MPY
MAC
MAC
MAC
MOVE
Difference Equation
yn ( ) = 2{ α[ x(
n)
– x(
n – 2)]
+ γyn ( – 1)
– βyn ( – 2)
}
X:(R0)
X0,Y1,A
X0,Y0,A
X0,Y0,A
X0,Y0,A
−α
γ
– β
α
Data Structures
Y:(R4)
Y:(R5)
DSP56001 Code
;Y1=x(n) (Input)
;X0=α
X:(R0)+,X0 Y:(R4),Y0 ;A=αx(n)
X:(R0)+,X0 Y:(R5)+,Y0 ;A=A-αx(n-2)
X:(R0)+,X0 Y:(R5),Y0 ;A=A+γy(n-1)
X:(R0)+,X0 Y1,Y:(R4)+ ;A=A-βy(n-2)
A,X1 A,Y:(R5)
;y(n)=2A (assumes scaling
; mode is set).
;X1 is Output.
Total Instruction Cycles
5 Icyc @ 20 MHz = 500ns
x(n-1)
x(n-2)
y(n-1)
y(n-2)
Figure 2-20 DSP56001 Code and Data Structures for Second-Order
Direct-Form Implementation of a Bandpass IIR Filter
MOTOROLA 2-25