
Philips Semiconductors
Audio Out
File: aout.fm5, modified 7/24/99
PRELIMINARY INFORMATION
9-3
9.6
SERIAL DATA FRAMING
The Audio Out unit can generate data in a wide variety of
serial data framing conventions.
Figure 9-2 illustrates the
notion of a serial frame. If POLARITY=1, a frame starts
on each positive edge of the AO_WS signal. If
CLOCK_EDGE=0, the parallel to serial converter sam-
ples AO_WS on a positive clock edge transition, and out-
puts the first bit (bit 0) of a serial frame on the next falling
edge of AO_SCK.
If CLOCK_EDGE = 1, the parallel to serial converter
samples AO_WS on the negative edge of AO_SCK,
while audio data is output on the positive edge, i.e. the
AO_SCK polarity would be reversed with respect to
Every serial frame transmits a single left and right chan-
nel sample to the D/A converter. The left and right sam-
ple data can be in an LSB first or MSB first form, at an
arbitrary bit position, and with an arbitrary length.
In MSB-first mode (DATAMODE = 0), the parallel to se-
rial converter assigns the value of LEFT[15] to the bit at
LEFTPOS in the serial frame. Subsequently, bits from
decreasing bit positions in the LEFT dataword, up to and
including LEFT[SSPOS], are transmitted in order.
In LSB-first mode (DATAMODE = 1), the parallel-to-seri-
al converter assigns the value of LEFT[SSPOS] to the bit
at LEFTPOS in the serial frame. Subsequent bits from
the LEFT data word, up to and including LEFT[15], are
transmitted in order.
Frame bits that do not belong to either LEFT[15:SSPOS]
or RIGHT[15:SSPOS] are set to zero. This ensures that
TM1100 can be used in combination with a D/A convert-
er which has a higher accuracy than the actual number
of transmitted bits.
Out unit MMIO registers would be set to transmit 16 bits
of stereo data via an I2S serial standard to an 18-bit D/A
converter with a 64-bit serial frame.
Table 9-3. Audio Out MMIO Clock & Interface Control
Field Name
Description
SER_MASTER
0
(RESET default), the D/A subsystem
is the timing master over the Audio
Out serial interface. AO_SCK and
AO_WS act as inputs.
1
TM1100 is the timing master over the
serial interface. AO_SCK and
AO_WS act as outputs. This mode is
required for 4,6 or 8 channel opera-
tion.
The SER_MASTER bit should only be
changed while Audio Out is disabled, i.e.
TRANS_ENABLE = 0.
FREQUENCY
Sets the clock frequency emitted by the
AO_OSCLK output. RESET default 0.
SCKDIV
Sets the divider used to derive AO_SCK
from AO_OSCLK. Set to 0..255, for divi-
sion by 1..256. RESET default 0.
WSDIV
Sets the divider used to derive AO_WS
from AO_SCK. Set to 0..511 for a serial
frame length of 1..512. RESET default 0.
Table 9-4. Audio Out Serial Framing Control Fields
Field Name
Description
POLARITY
0
serial frame starts with a AO_WS
negedge (RESET default)
1
serial frame starts with a AO_WS
posedge
This bit should NOT be changed during
operation of Audio Out, i.e.only update this
bit when TRANS_ENABLE = 0.
LEFTPOS(9)
Denes the bit position within a serial frame
where the rst data bit of the left channel is
placed. Default 0.
RIGHTPOS(9)
Denes the bit position within a serial frame
where the rst data bit of the right channel is
placed. Default 0.
DATAMODE
0
MSB rst (RESET default)
1
LSB rst
SSPOS
Start/Stop bit position. Default 0.
If DATAMODE=MSB rst, SSPOS deter-
mines the bit index (0..15) in the parallel
word of the last data bit. Bits 15 (MSB) up
to/including SSPOS are generated. All
other bits are output as zero.
If DATAMODE=LSB rst, SSPOS deter-
mines the bit index (0..15) in the parallel
word of the rst data bit. Bits SSPOS up to/
including 15 are generated. All other bits
are output as zero.
CLOCK_EDGE 0
the parallel to serial converter samples
AO_WS on positive edges of AO_SCK
and outputs data on the negative edge
of AO_SCK (RESET default).
1
the parallel to serial converter samples
AO_WS on negative edges of AO_SCK
and outputs data on positive edges of
AO_SCK.
WS_PULSE
0
emit 50% AO_WS (RESET default).
1
emit single AO_SCK cycle AO_WS
(this bit is ignored if SER_MASTER=0)
In case of 6 channel audio (see
SectionWS_PULSE should be set to ‘1’
SFDIV
Table 9-4. Audio Out Serial Framing Control Fields
Field Name
Description