Datasheet

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SLES105B − FEBRUARY 2004 − REVISED NOVEMBER 2006
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46
TDMCA Mode Determination
The PCM1792A 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 54 shows the LRCK and BCK timing that determines the TDMCA mode. The PCM1792A 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
BCK
LRCK
2 BCK
TDMCA Frame
Command
Accept
Figure 54. LRCK and BCK Timing of Determination TDMCA Mode
TDMCA Terminals
TDMCA requires six signals, of which four signals are for command and audio data interface, and one pair is
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
TDMCA
NAME
PROPERTY DESCRIPTION
LRCK LRCK input TDMCA frame start signal. It must be the same as the sampling frequency.
BCK BCK input
TDMCA clock. Its frequency must be high enough to communicate a TDMCA frame within an LRCK
cycle.
DATA DI input TDMCA command and audio data input signal
MDO DO output TDMCA command data 3-state output signal
MC DCI input TDMCA daisy-chain input signal
MS DCO output TDMCA daisy-chain output signal
Device ID Determination
The TDMCA mode also supports a multichip implementation in one system. This means a host controller (DSP)
can simultaneously support several TDMCA devices, which can be of the same type or different types, including
PCM devices. The PCM devices are categorized as IN device, OUT device, IN/OUT device, and NO device.
The IN device has an input port to get audio data, the OUT device has an output port to supply audio data, the
IN/OUT device has both input and output ports for audio data, and the NO device has no port for audio data
but needs command data from the host. A DAC is an IN device, an ADC is an OUT device, a CODEC is an
IN/OUT device, and a PLL is a NO device. The PCM1792A is an IN device. For the host controller to distinguish
the devices, each device is assigned its own device ID by the daisy chain. The devices obtain their own device
IDs automatically by connecting their DCI to the DCO of the preceding device and their DCO to the DCI of the
following device in the daisy chain. The daisy chains are categorized as the IN chain and the OUT chain, which
are completely independent and equivalent. Figure 55 shows an example daisy chain connection. If a system
needs to chain the PCM1792A and a NO device in the same IN or OUT chain, the NO device should be chained
at the back end of the chain because it does not require any audio data. Figure 56 shows an example of TDMCA
system including an IN chain and an OUT chain with a TI DSP. For a device to get its own device ID, the DID
signal must be set to 1 (see the Command Field section for details), and LRCK and BCK must be driven in the
TDMCA mode for all PCM devices which are chained. The device at the top of the chain knows its device ID
is 1 because its DCI is fixed HIGH. Other devices count the BCK pulses and observe their own DCI signal to
determine their position and ID. Figure 57 shows the initialization of each device ID.