Datasheet

TDMCA Terminals
Device ID Determination
INDevice
DCI
DCO
OUTDevice
DCI DCO
IN
OUT
IN/OUT
Device
INChain
OUTChain
INDevice
OUTDevice
DCI
DCO
DCI DCO
DCIi
DCIo
DCOi
DCOo
IN
OUT
DCIi
DCIo
DCOi
DCOo
NODevice
DCI
DCO
NODevice
DCI DCO
NODevice
NODevice
DCI
DCO
DCI DCO
IN/OUT
Device
¼
¼
¼
¼
¼
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 LRCK Input
frequency
TDMCA clock; its frequency must be high enough to communicate a
BCK BCK Input
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
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
46 Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): PCM1795