PDSP16510A MA
not go active until this priming has occurred. The DOS priming
strobes must be enabled by the DEN input, unless the device
has been configured in one of the multiple device modes ( See
section on Multiple Device Systems ).
The state of the DEN input at the end of a transform is
used to control the transition of the active going edge of the
DAV output with respect to the DOS strobes. The latter are
then used to transfer data from the device to the next system
component. If the DEN input is tied low in a single device
system, the active going DAV transition will be internally
synchronised to the rising edge of a DOS clock. If DEN is not
tied low it must be guaranteed to be low at the end of the
internal transform operation for this synchronization to occur.
Since there is no external indication of this event, the user
must take care to only allow DEN to go high whilst DAV is
active, if this DAV synchronous mode is needed.
timing is given in Table 2. It should be noted that the DOS input
MUST be continually present before DAV goes active. If this
is not the case the DAV output will not go active at the correct
time, and the internal output circuitry will not be primed. Once
DAV is active, however, it is possible for DOS to be irregular,
and DEN can be used to inhibit the action of the output strobe
as discussed previously. For the correct operation of the
device the user must ensure that DOS becomes continuous
and DEN remains low once DAV goes in-active.
When continuously transforming data such that new
outputs are internally available before the previous block has
been completely dumped, then DAV would normally stay
active and give no indication that one block dump had been
finished and another block started. Additional internal circuitry
is, however, provided to ensure that DAV goes inactive for one
DOS high time, thus supplying an inter block marker.
SYNCHRONIZED DAV OPERATION
In the DAV synchronised mode the first rising edge of the
DOS clock, after DAV has gone active, must be used to
transfer the first transformed sample from the output pins to
the next system component. It should be noted that the output
buffer will have been primed before the active DAV transition,
since DOS must be a continuous clock, and there is then no
delay before the first output becomes valid. The DAV output
can be used as a clock enable for this next device, and
transfers will continue in normal sequential order until the
required data has been dumped. DAV will then go inactive in
response to the last DOS edge which was used to transfer
data to the next device.
This mode of automatically dumping data when it is ready
finds applications in real time data flow systems, and detailed
ASYNCHRONOUS DAV MODE
If DEN is not active in a single device when the transform
is complete, then the device will wait for DEN to go active
before any data is dumped. This mode is suitable for applica-
tions in which output processing is under the control of a
remote host, such as a general purpose digital signal proces-
sor. The DAV output will then go active as soon as the output
buffer is full, and will not be synchronised to the DOS edge. In
such systems the DOS strobe may not necessarily be present
at this time. Table 3 gives the relevant timing information.
In this host controlled dump mode the PDSP16510 waits
for the host to activate the DEN input after DAV has gone
active. DEN then functions as an enable for the host produced
data strobes on the DOS pin. DEN may either stay active for
the complete transfer, or may be used to enable each DOS
16510A
Characteristic
†
†
†
†
†
†
Output Enable Time
Output Disable Time
Data Delay Time ( 30 pf load )
Data Hold Time
DAV active Delay Time ( 30 pf load )
DAV in active Delay Time ( 30 pf load )
Symbol
T
LZ
T
HZ
T
DD
T
DH
T
VD
T
VI
2
1
1
10
10
Min
Max
15
15
15
Units
ns
ns
ns
ns
ns
ns
Table 2. Output Timing with DEN tied low. ( Advanced Data )
9
MITEL [ MITEL NETWORKS CORPORATION ]
