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TDMCA Terminals

Device ID Determination

INDevice

OUTDevice

OUT

IN/OUT

Device

INChain

OUTChain

INDevice

OUTDevice

OUT

NODevice

IN/OUT

Device

PCM1795

SLES248 – MAY 2009 ........................................................................................................................................................................................................ www.ti.com

TDMCA requires six signals: four signals are for the command and audio data interface, and one pair for

daisy-chaining. These signals can be shared as shown in Table 15. The DO signal has a 3-state output so that it

can be connected directly to other devices.

Table 15. TDMCA Terminals

TERMINAL NAME

TDMCA NAME

PROPERTY

DESCRIPTION

TDMCA frame start signal; it must be the same as the sampling

LRCK

Input

frequency

TDMCA clock; its frequency must be high enough to communicate a

BCK

Input

TDMCA frame within an LRCK cycle

DATA

Input

TDMCA command and audio data input signal

MDO

Output

TDMCA command data 3-state output signal

DCI

Input

TDMCA daisy-chain input signal

DCO

Output

TDMCA daisy-chain output signal

TDMCA mode also supports a multichip implementation in one system. This capability means that 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 either IN devices, OUT devices, IN/OUT

devices, and NO devices. The IN device has an input port to receive 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 requires 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 PCM1795 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 the DCI to the DCO of the preceding device and the

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 62 shows an example daisy-chain

connection. If a system must chain the PCM1795 and a NO device in the same IN or OUT chain, the NO device

must be chained at the back end of the chain because it does not require any audio data. Figure 63 shows an

example 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 that 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 the

respective DCI signal to determine ID and position in the chain. Figure 64 shows the initialization of each device

ID.

Figure 62. Daisy-Chain Connection Example

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