6-4
Channel Interface
6.2.1 Asynchronous Mode
The timing for this mode is shown in
Figure 6.2
. The decoder asserts the
AREQn or VREQn signal when it is ready for more audio or video data.
Both the AREQn and VREQn requests are used for elementary streams
and A/V PES streams from a transport decoder. Only the AREQn is used
for program stream inputs.
The connecting device places the requested data on the CH_DATA[7:0]
bus and asserts and deasserts its AVALIDn or VVALIDn output in
response. Again, both VALIDn inputs are used for elementary streams
and A/V PES streams; only the AVALIDn input is used for program
stream inputs. A byte of data is strobed into the input FIFO of the L64105
on each rising edge of the VALIDn signal while its corresponding REQn
signal is low. One extra byte can be strobed in after the REQn signal is
deasserted. Note that both the AREQn and VREQn signals can be
asserted at the same time. In that case, it is up to the connecting device
to decide whether to strobe audio or video in.
Figure 6.2
Asynchronous Channel Interface Timing
The constraints of this mode are:
1.
AVALIDn and VVALIDn should never be low at the same time. The
valid byte on CH_DATA[7:0] is either audio or video.
2.
Any VALIDn rising edge to VALIDn rising edge must be separated by
≥
3Tc. This allows the synchronizing logic of the L64105 time to
resynchronize, and the input channel FIFO time to deassert the
AREQn/VREQn signals and prevent overflow conditions.
AVALIDn
AREQn
VVALIDn
VREQn
CH_DATA
1. One extra byte okay for asynchronous AREQn/VREQn.
1
1