0AMA datasheet(17/23 Pages) MITEL

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PDSP16510A MA

than 1024 points are to be performed simultaneously. It

changes the LFLG logic and allows sampling rates up to the

system clock rate to be achieved with multiple output proces-

sors.

BIT 11

When this bit is set the PDSP16510 will not generate DAV

until 24 DOS clocks after data was actually valid. In this case

the output tri-state drivers will be enabled at the correct time,

even though the DAV signal was not externally valid. Host

controlled dumping should not be used.

BIT 12

When this bit is set in the single device mode, the INEN

input is a simple load enable signal. When it is reset an INEN

edge is needed at the end of a load sequence before a new

one can commence.

When it is reset in a multiple device mode it has no

action, but when it is set it will cause the DEF high going edge

to also initiate a load operation.

BIT 14:13

These bits allow four dump size options to be provided.

Individual frequency bins are not accessible.

BIT 15

Under normal circumstances DAV would be expected to

go invalid when a transform has been dumped. In some

applications, however, it may be necessary to read the outputs

more than once. When this bit is set, DAV will remain valid until

the next INEN input, and will indicate that the transformed data

still remains in the internal buffer. As soon as the next INEN is

received the transformed data will be overwritten. Whilst DAV

remains active the output tri-states will be enabled.

WINDOW OPERATORS

Since only a finite segment of a signal can be observed and

processed at any one time, it is impossible to obtain pure

spectral lines. Discontinuities are introduced at the bounda-

ries of the observation interval which lead to spectral leakage.

Windows are weighting functions applied to the data in order

to reduce these discontinuities at the boundaries.

In the time domain the signal has to be observed through

a finite window as a matter of accord. This is in fact equivalent

to multiplying the signal with a set of uniform weights i.e. a

rectangular window operator. In the frequency domain the

spectrum of the data will be the spectrum of this weighting

function shifted to the sinusoidal frequencies of the compo-

nents in the data.

The rectangular window has a Fourier Transform which is

a SINC(X) function. This has sidelobes which are only 13dB

down from the main lobe. This severely limits the dynamic

range of the system since a second sinusoid in close proximity

would have its main lobe swamped by this side lobe. This

would occur if its amplitude was a mere 13dB down from the

first sinusoid.

Window operators are thus mathematically constructed

to cancel these sidelobes as far as possible. Unfortunately this

is normally done at the expense of making the main lobe

spread over more frequency bins. This reduces the ability of

the system to resolve two frequencies, and can only be

inputs. When data is from a single source, and no overlaps are

needed, only the real input should be used. If 50% or 75%

overlaps are needed from a single source of real data, the

device always expects blocks to be simultaneously loaded. An

external FIFO is then needed to supply data to the real inputs

after a delay of one block. Each block is thus loaded twice,

firstly through the Auxiliary inputs and then through the Real

inputs.

BIT 10:9

These bits define a single device system, or one of three

multiple device possibilities. The choice between the first and

second multiple device mode is dependent on the transform

size and the sampling rate needed. The third mode should

only be used when overlapped multiple transforms with less

Table 6. Mode Control Bit Allocations

BITS

Dec'

OPTION

2:0

000

16 x 16 COMPLEX

001

4 x 64 COMPLEX

010

256 COMPLEX

011

1024 COMPLEX

100

8 X 64 REAL

101

2 X 256 REAL

110

2 X 1024 REAL

111

NOT USED

SHIFT 3 PLACES AFTER PASS1

ALWAYS SHIFT 2 PLACES

5:4

RECTANGULAR

HAMMING WINDOW

BLACKMAN-HARRIS

INVERSE TRANSFORM

8:6

000

NO OVERLAP

001

50% OVERLAP

010

50% OVERLAP AND DIS

÷ 2

011

75% OVERLAP

100

75% OVERLAP AND DIS

÷ 4

101

DUAL SOURCE, NO OVERLAP

110

DUAL SOURCE, 50% OVERLAP

111

DUAL SOURCE, 75% OVERLAP

10:9

SINGLE DEVICE

N DEVICES, CONCURRENT I/O

N DEVICES, LOAD-TRANS-DUMP

SPECIAL MULTIPLE TRANSFORM

DAV NOT DELAYED

24 CLK DAV DELAY

INEN EDGE ACTIVATED

INEN IS SIMPLE ENABLE

14:13

O/P FIRST QUARTER

O/P FIRST HALF

O/P LAST HALF

O/P ALL RESULTS

NORMAL DAV

KEEP DAV ACTIVE TILL INEN

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