PDSP16515GCPR datasheet(23/27 Pages) MITEL

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PDSP16515A

DOS can now be switched on for at least one pulse (but may

be more), and the sequence of events as described earlier

(from point No 3.3) will start. DEN can then be made active,

whereby a further 4 DEN-Enabled DOS pulses will be required

before data is seen on the output pins. This is the situation

shown in table 3.

Alternatively, DEN and DOS could be made to operate on the

same cycle. In this case data will appear on the output pins on

the 5th DOS pulse (the first would not actually require the

presence of DEN, but the 2nd, 3rd, 4th and 5th would)

(4.3) 1024 point transforms, single device mode.

In the case of 1024 point transforms, the internal RAM is no

longer operated in the manner described in section 2. The

RAM is instead totally dedicated to one operation at a time.

Thus data for a transform will be loaded, and all 12 out of 12

SCLK cycles will be available for the transfer of input data to

the RAMs. During the transfrom no transfers from the input to

the RAM or from the RAM to the output are possible. This is

why DIS and DOS can be equal to SCLK for 1024 point

transforms.

If 1024 point transforms are being performed and the

device is programmed as a single device, then

"asynchronous" operation of DAV is possible as described

earlier for transform sizes less than 1024 points. If DEN is

inactive at the time the transform has finished calculating, then

DAV will be made to go active regardless of the state of DOS.

Although 6 SCLK cycles do not have to be waited for as in

section 3.2, a transition has to be made from the transform

controlling the internal RAM to the output circuits cntrolling it.

This operation plus the time taken to advance data from the

RAMs to the output buffer takes exactly 4 SCLK cycles.

Hence the sequence of events is exactly as described in

section 3, except that section 3.3 should read 4 SCLK cycles

rather than 6. The analysis of sections 4.1 nad 4.2 are also true

if the 6 SCLK cycle time is substituted with 4 SCLK cycles.

Dummy DOS Strobes After DEF

In addition to the dummy DOS strobes needed prior to

dumping data, it is necessary to provide at least 4 DOS strobes

after DEF has gone inactive, but before DAV goes active.

These initialise the internal address counters and do not rely

on DEN also being active. They are needed every time DEF

has been used to change the operating mode.

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