SRC4184 Datasheet, PDF (36/40 Pages) Burr-Brown (TI) – 4-Channel, Asynchronous Sample Rate Converter

SRC4184
SBFS026A − JUNE 2004 − REVISED JULY 2004
TDM APPLICATIONS
The SRC4184 supports a TDM output mode, which allows
multiple devices to be daisy-chained together to create a
serial frame. Each device occupies one sub-frame within
a frame, and each sub-frame carries two channels (Left
followed by Right). Each sub-frame is 64 bits long, with 32
bits allotted for each channel. The audio data for each
channel is left-justified within the allotted 32 bits. Figure 16
illustrates the TDM frame format, while Figure 15 shows
TDM input timing parameters, which are listed in the
Electrical Characteristics table of this data sheet.
LRCKO
BCKO
TDMI
t_LROS
t_LROH
t_TDMS
t_TDMH
Figure 15. Input Timing for TDM Mode
The frame rate is equal to the output sampling frequency,
f_s. The BCKO frequency for the TDM interface is N × 64f_s,
where N is the number of SRC sections included in the
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daisy-chain. For Master mode, the output BCKO
frequency is fixed to the reference clock input frequency.
The number of devices that can be daisy-chained in TDM
mode is dependent upon the output sampling frequency
and the bit clock frequency, leading to the following
numerical relationship:
Number of Daisy-Chained SRC Sections = (f_BCKO/f_s)/64
Where:
f_BCKO = Output Port Bit Clock (BCKO), 27MHz maximum
f_s = Output Port Sampling (or LRCKO) Frequency, 212kHz
maximum.
This relationship holds true for both Slave and Master
modes.
Figure 17 and Figure 18 illustrate typical connection
schemes for TDM mode. Although the TMS320C671x
DSP family is shown as the audio processing engine in
these figures, other TI digital signal processors with a
multi-channel buffered serial port (McBSP) may also
function with this arrangement. Interfacing to processors
from other manufacturers is also possible. Refer to the
timing diagrams this data sheet, along with the equivalent
serial port timing diagrams shown in the DSP data sheet
to determine compatibility.
LRCKO
BCKO
SDOUT
Left
Right
Sub−Frame 1
Left
Right
Sub−Frame 2
One Frame = 1/f_s
Left
Right
Sub−Frame N
N = Number of Daisy−Chained Devices
One Sub−Frame contains 64 bits, with 32 bits per channel.
For each channel, the audio data is Left−Justified, MSB−first format, with the word length determined by the OWL[1:0] pins/bits.
Figure 16. TDM Frame Format
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