PNX1300/01/02/11 Data Book
Philips Semiconductors
9-2
PRELIMINARY SPECIFICATION
AO_WS, left & right data in a frame).
LSB first, with 1
–
16-bit data per channel.
Complex serial frames of up to 512 bits/frame.
Up to 8 channels of audio output.
Table 9-1. AO unit external signals
9.3
SUMMARY OF OPERATION
The AO unit consists of three major subsystems, a pro-
grammable sample clock generator, a DMA engine and
a data serializer.
The DMA engine reads 16 or 32-bit samples from mem-
ory using a double buffered DMA approach. The
DSPCPU initially assigns two full sample buffers contain-
ing an integral number of samples for all active channels.
The DMA engine retrieves samples from the first buffer
until exhausted and continues from the second buffer,
while requesting a new first sample buffer from the
DSPCPU, etc.
The samples are given to the data serializer, which
sends them out in a MSB first or LSB first serial frame for-
mat that can also contain 1 or 2 codec control words of
up to 16 bits. The frame structure is highly programmable
by a series of MMIO fields.
9.4
INTERNAL CLOCK SOURCE
Figure 9-1
illustrates the different clock capabilities of the
AO unit. At the heart of the clock system is a square
wave DDS (Direct Digital Synthesizer). The DDS can be
Signal
Type
Description
AO_OSCLK
OUT
Over sampling clock. Can be programmed
to emit any frequency up to 40 MHz, with
sub-Hz resolution. Intended for use as the
256 or 384f
s
oversampling clock by the
external D/A conversion subsystem.
When AO is programmed to act as a
serial interface timing slave (RESET
default), AO_SCK acts as input. It
receives the serial clock from the exter-
nal audio D/A subsystem. The clock is
treated as fully asynchronous to the
PNX1300 main clock.
When AO is programmed to act as
serial interface timing master, AO_SCK
acts as output. It drives the serial clock
for the external audio D/A subsystem.
Clock frequency is a programmable
integral divide of the AO_OSCLK fre-
quency.
AO_SCK is limited to 22 MHz. The sam-
ple rate of valid samples embedded within
the serial stream is limited by the
AO_SCK maximum frequency and the
available highway bandwidth.
When AO is programmed as the serial-
interface timing slave (RESET default),
AO_WS acts as an input. AO_WS is
sampled on the opposite AO_SCK
edge at which AO_SDx are asserted.
When AO is programmed as serial-
interface timing master, AO_WS acts
as an output. AO_WS is asserted on
the same AO_SCK edge as AO_SDx.
AO_WS is the word-select or frame-sync
signal from/to the external D/A sub-
system. Each audio channel receives 1
sample for every WS period.
AO_WS can be set to change on
AO_OSCLK positive or negative edges by
the CLOCK_EDGE bit.
AO_SCK
IO
AO_WS
IO
AO_SD1
OUT
Serial data to stereo external audio D/A
subsystem. AO_SD1 can be set to
change on AO_OSCLK positive or nega-
tive edges by the CLOCK_EDGE bit.
Serial data to stereo external audio D/A
subsystem. AO_SD2 can be set to
change on AO_OSCLK positive or nega-
tive edges by the CLOCK_EDGE bit.
Serial data to stereo external audio D/A
subsystem. AO_SD3 can be set to
change on AO_OSCLK positive or nega-
tive edges by the CLOCK_EDGE bit.
Serial data to stereo external audio D/A
subsystem. AO_SD4 can be set to
change on AO_OSCLK positive or nega-
tive edges by the CLOCK_EDGE bit.
AO_SD2
OUT
AO_SD3
OUT
AO_SD4
OUT
Table 9-1. AO unit external signals
Signal
Type
Description
FREQUENCY
AO_OSCLK
AO_SCK
AO_WS
div N+1
SCKDIV
div N+1
Square Wave DDS
9
×
DSPCPUCLK
AO_SDx
Parallel to Serial Converter
16
16
LEFT[15:0]
RIGHT[15:0]
AO_CC[31:0]
(e.g. 64
×
f
s
)
WSDIV
31
0
7
0
0
8
(e.g. 256
×
f
s
)
32
Figure 9-1. AO clock system and I/O interface
SER_MASTER