Motorola MPC823e - Page 511

Communication Processor Module
MOTOROLA MPC823e REFERENCE MANUAL 16-57
DSP
COMMUNICATION
16
PROCESSOR MODULE
16.3.4.5.3 FIR6 Parameter Packet. The FIR6 parameter packet is composed of seven
16-bit half-words and described in the table below.
16.3.4.6 IIR–REAL C, REAL X, REAL Y. The IIR function implements a basic BIQUAD IIR
filter with six real coefficients, real input samples, and real outputs. The input data is in a
circular buffer with size M+1 and the output data is in a circular buffer with size N+1. Several
stages of the BIQUAD filter can be cascaded by specifying an iteration count greater than
one and concatenating the filter coefficients into one vector.
16.3.4.6.1 Coefficients and Sample Data Buffers. The coefficients vector occupies six
16-bit half-words in memory and C(0) is stored in the first location. C(1) is only used in the
last stage of a cascaded IIR filter. The sample input buffer is a cyclic buffer that contains
M+1 bytes. Each sample is a 16-bit half-word and the new sample is stored in the address
that follows the previous sample. The output buffer is a cyclic buffer that contains N+1 bytes
and the new output is stored in the address that follows the previous one.
Table 16-12. FIR6 Parameter Packet
ADDRESS NAME DESCRIPTION
Half-word 1 I Number of Iterations-1 (0 = one iteration)
Half-word 2 K Number of TAPs-1. The number of taps must be a multiple of 2.
Half-word 3 CBASE Filter Coefficients Vector Base Address Pointer
Half-word 4 M Samples Buffer Size-1. The minimum sample buffer size is 4(2 samples).
Half-word 5 XYPTR Pointer to a structure composed of the input sample data pointer and the output
buffer pointer
Half-word 6 N Output Buffer Size-1. The minimum output buffer size is 8 (2 outputs).
Half-word 7 RES Reserved
Figure 16-22. IIR Implementation Example
C(4)C(2)
C(1)
T
T
∑
X(N)
Y(N)
C(0)
C(5)
{REAL}
{REAL}
{REAL}
∑
C(3)
∑
∑