PCM1791A Datasheet, PDF (44/58 Pages) Texas Instruments – 24-BIT, 192-kHz SAMPLING, ADVANCED SEGMENT, AUDIO STEREO DIGITAL-TO-ANALOG CONVERTER

PCM1791A
SLES071A − MARCH 2003 − REVISED JANUARY 2004
TDMCA INTERFACE FORMAT
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The PCM1791A supports the time-division-multiplexed command and audio (TDMCA) data format to simplify the
host control serial interface. The TDMCA format is designed not only for the McBSP of TI DSPs but also for any
programmable devices. The TDMCA format can transfer not only audio data but also command data, so that it can
be used together with any kind of device that supports the TDMCA format. The TDMCA frame consists of a command
field, extended command field, and some audio data fields. Those audio data are transported to IN devices (such
as a DAC) and/or from OUT devices (such as an ADC). The PCM1791A is an IN device. LRCK and BCK are used
with both IN and OUT devices so that the sample frequency of all devices in a system must be the same. The TDMCA
mode supports a maximum of 30 device IDs. The maximum number of audio channels depends on the BCK
frequency.
TDMCA Mode Determination
The PCM1791A recognizes the TDMCA mode automatically when it receives an LRCK signal with a pulse duration
of two BCK clocks. If the TDMCA mode operation is not needed, the duty cycle of LRCK must be 50%. Figure 52
shows the LRCK and BCK timing that determines the TDMCA mode. The PCM1791A enters the TDMCA mode after
two continuous TDMCA frames. Any TDMCA commands can be issued during the next TDMCA frame after the
TDMCA mode is entered.
Pre-TDMCA Frame
TDMCA Frame
Command
Accept
LRCK
2 BCK
BCK
Figure 52. LRCK and BCK Timing for Determination of TDMCA Mode
TDMCA Terminals
TDMCA requires six signals, four of which are for command and audio data interface, and one pair of signals which
are for daisy chaining. Those signals can be shared as in the following table. The DO signal has a 3-state output so
that it can be connected directly to other devices.
TERMINAL
NAME
LRCK
BCK
DATA
MDI
MC
MS
TDMCA
NAME
LRCK
BCK
DI
DO
DCI
DCO
PROPERTY
DESCRIPTION
input
input
input
output
input
output
TDMCA frame start signal. It must be the same as the sampling frequency.
TDMCA clock. Its frequency must be high enough to communicate a TDMCA frame within an LRCK
cycle.
TDMCA command and audio data input signal
TDMCA command data 3-state output signal
TDMCA daisy-chain input signal
TDMCA daisy-chain output signal
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