PDSP16510A MA

7

Characteristic

Data In set up Time

Data In Hold Time

INEN active going set up

INEN active Hold Time

INEN in-active Hold Time to ensure no load

INEN in-active going set up for no load operation

Delay to LFLG going active ( 30 pf load )

Delay to LFLG going in-active ( 30 pf load )

Min time to INEN low in edge mode

input and output buffering in addition to working memory. The

device is then configured in a mode with separate load,

transform and dump operations. The internal arrangement is

shown in Fig. 5. The support of an external input buffer is

needed if incoming samples are not to be lost whilst a

transform is in progress. This is loaded at the sample clock

rate and transferred to the FFT processor as quickly as

possible. In this mode the PDSP16510 always expects to

receive 1024 words, regardless of the amount of block over-

lapping. Data stored internally cannot be re-used when block

overlapping is required, and data from the external buffer must

be re-read as necessary.

Fig. 6 illustrates a typical 1024 point system with an input

buffer which supports complex input data. The input buffer

can be provided by a PDSP16540 Bucket Buffer without the

need for any external control logic. It supplies RAM for 1024

x 32 complex words, and allows transfers to the FFT Proces-

sor at the full system clock rate. The PDSP16540 also sup-

ports the standard 50% and 75% data block overlapping, but

in addition allows the user to define the amount of overlap to

within 32 words.

If no incoming data is to remain un-processed, the user

must ensure that the time taken to acquire sufficient data to

instigate a new transform is greater than or equal to the

transformation time itself. The latter can be calculated from

Table 1. Advanced Timing Information with Continuous Inputs.

Table 4, once the system clock rate has been defined. When

1024 point transforms are performed, both the time to read

data from the input buffer, and also the time to dump data,

must be included in the calculation to determine the minimum

time in which data can be loaded into the external buffer.

The peak transfer rate is limited by the characteristics of

the I/O circuits, but can be greater than the sampling rate

which is determined by the transform time. When load and

dump operations are not concurrent with transform operations

( as in the 1024 point modes ), then the maximum I/O rate is

equal to the system clock rate, Ø. When other transform sizes

are specified, the sampling rate, S, is reduced by a factor F.

This is defined below where Ø is in MHz and L is the system

clock low time in nanoseconds;

S = FØ,

where F =

4

6 + 0.001ØL

F is typically 0.66 and applies to all transforms except for those

of 1024 points, even if INEN is driven such that concurrent

operations do not actually occur. If this causes a system

limitation in a single device application, then the device can be

configured for pseudo, Mode 2, multiple device operation.

Separate load, transform, and then dump operations will then

always occur, but DEN must be low when a transform is

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Symbol

Min

Max

Units

T

SD

10

ns

T

HD

0ns

T

SA

8ns

T

HA

0ns

T

HI

2ns

T

SI

8ns

T

FH

10

ns

T

FL

10

ns

T

ED

15

ns

16510A