PDSP16256AC datasheet(7/28 Pages) MITEL

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PDSP16256

Figure. 5 Filter network diagram

Single Filter Options

When operating as a single filter the device accepts data

on the 16-bit DA bus at the selected sample rate, see

Figs. 5 and 6. Results are presented on the 32-bit F bus,

which may be tristated using the OEN input. Signal OEN is

registered onto the device and does not therefore take

effect until the first SCLK rising edge. Devices may be

cascaded this allows filters with more taps than available

from a single device. To accomplish this two further

buses are utilised. The DB bus presents the input data to

the next device in cascade after the appropriate delay,

while, partial results are accepted on the X bus.

Single filter mode is selected by setting control register bit

15 to a one. The required filter length is then selected

using control register bits 14 and 13 as summarised in

Table 3. The options define the number of times each

multiplier accumulator is used per sample clock period.

This can be once, twice, four times, or eight times.

In addition a normal/decimate bit (CR12) allows the filter

length to be doubled at any sample rate. This is possible

when the filter coefficients are selected to produce a low

pass filter, since the filtered output would then not contain

the higher frequency components present in the input.

The Nyquist criterion, specifying that the sampling rate

must be at least double the highest frequency compo-

nent, can still then be satisfied even though the sampling

rate has been halved.

The system clock latency for a single device is shown in

Table 3. This is defined as the delay from a particular data

sample being available on the input pins to the first result

including that input appearing on the output pins. It does

not include the delay needed to gather N samples, for an

N tap filter, before a mathematically correct result is

obtained.

Input

Output

Filter

Setup

14 13 12

Rate

Length

Latency

SCLK

16 Taps

SCLK

SCLK/2

32 Taps

SCLK/2

32 Taps

SCLK/2

SCLK/4

64 Taps

SCLK/4

64 Taps

SCLK/4

SCLK/8

128 Taps

SCLK/8

128 Taps

Table 3 Single Filter options

Figure. 6 Single Filter bus utilisation

DA15:0

F31:0

OEN

NETWORK

DUAL

MODE

SINGLE

MODE

MUX

DB15:0

X31:0

DATA

DELAY LINE

DATA

OUT

COEFF

RAM

ADDER

Z21

DATA

DELAY LINE

COEFF

RAM

ADDER

Z21

DATA

DELAY LINE

COEFF

RAM

ADDER

Z21

DATA

DELAY LINE

COEFF

RAM

ADDER

Z21

ACCUMULATE

EXPANSION

DATA

RESULT

OUT

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