PDSP16510

9

input. When DEN and DOS are both active an internal read

operation occurs, and an address generator is incremented.

DAV goes in-active in response to the DOS edge needed to

read the last output, unless Bit 15 in the Control Register is set.

In this case DAV goes in-active when the next INEN edge is

received for reasons given later.

In host controlled systems the time to dump data could be

longer than the transform time. The dump time in such a

system will dictate the maximum sampling rate that can be

used without the loss of incoming data. In the 1024 point

mode, when the loss of data is not important, the PDSP16510

is designed to not accept new data until the previous results

have been dumped. Such a system needs no input buffer, and

INEN can be permanently tied low if the edge activated mode

is not in use. If the loss of data is to be avoided an input buffer

is needed and the host must have received all the results

before a new block of data has been loaded into the buffer.

For 256 point transforms, with host controlled dumping,

it is still possible to overlap load and dump operations. The

maximum dump times, however, must be less than the load

times to avoid data corruption. Previously converted outputs

will be actually corrupted, rather than inputs simply not being

used.

If the loss of incoming data is not important, the device

can be forced to do separate load, transform, and then dump

operations. The corruption of results will then never occur, no

matter what dump time is taken. This can be achieved by

ensuring that INEN is not active between loading a block of

data and completing the dump of the results from that data.

The same ends can be achieved if the INEN edge activated

mode ( Bit 12 reset ) is used, and the inverted DAV edge is

used to drive the INEN input. This then initializes a new load

operation only when the previous dump has been completed.

Results are transferred from the device with the rising

edge of the DOS strobe when DEN is active. This is consistent

with using the device in a data flow architecture, as is com-

monly employed in data processing systems. In a typical

microprocessor based system, however, data is normally

expected to become valid before the end of the data strobe

produced by the processor. It is thus necessary for the user

to provide a ‘dummy’ data strobe in order to transfer data to

the outputs which can then be read by the host during the next

data strobe. In addition further ' dummy ' strobes are needed

each time DAV goes active in order to prime the output

circuitry. The actual output sequence is given in Table 3 for a

single device systemand is described more fully in "user notes

- stopping DOS".

GENERAL DUMP CONSIDERATIONS

The tri-state drivers on the output buses are only enabled

when both DAV and DEN are active. When DEN is tied

permanently low the output bus will start to become valid from

the DOS edge which also generates the DAV output. The next

DOS edge can then be used to transfer the first output to the

next device. When DEN is driven low in response to the DAV

output, the outputs start to become valid when DEN goes low.

The Scale Tag outputs become valid at the same time as data,

and when enabled will continue to indicate the correct value

until all frequency bins have been dumped. If at any time

during the dump operation DEN goes in- active, then both the

Table 3. Host Controlled Output Timing. ( Advanced Data )

Characteristic

Symbol

Min

Max

Units

DEN Set Up Time

T

PS

10

ns

Host Strobe Width

T

PW

10

ns

DEN Hold Time

T

PH

5

ns

DAV in-active going Delay ( 30 pf load )

T

VI

10

ns

Output Enable Time ( see Fig 13 )

T

LZ

10

ns

Output Data Delay Time ( 30 pf load )

T

DD

15

ns

Output Disable Time ( see Fig 13 )

T

HZ

10

ns

Read Cycle Time

T

RC

25

ns

Old Data Hold Time

T

OH

2

ns

16510A,A0,B0,C0

DEN

DATA

O/P

DAV

O/P 1

O/P 2

DOS

O/P 1

S3:0

Scale Tag Value

Scale Tag Value

O/P N

Dummy Strobes

Un-defined

Un-defined

In this zone SCLK and DOS requirements have to be met - See "User Notes - stopping DOS"

(1)

(2)

(3)

(4)