PCM1795DB datasheet(49/68 Pages) TI2

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Pre-TDMCA Frame

BCK

LRCK

TDMCAFrame

Command

2BCKs

FSX

FSR

CLKX

CLKR

TI DSP

Host

Controller

IN Device

PCM1795

LRCK

BCK

DCI

VDD

Device ID = 1

DCO

PCM1795

www.ti.com

SLES248A – MAY 2009 – REVISED MARCH 2015

8.2.4 TDMCA Interface Format

The PCM1795 device supports the time-division-multiplexed command and audio (TDMCA) data format to

simplify the host control serial interface. TDMCA format is designed not only for the multichannel buffered serial

port description (McBSP) of TI DSPs but also for any programmable devices. 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

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 PCM1795 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.

Figure 68. TDMCA Diagram

8.2.4.1 Design Requirements

•

Control: TDMCA control information

•

Audio Input: TDMCA input with LRCK signal with a pulse of two BCK clocks

•

Audio Output: I/V output circuitry

8.2.4.2 Detailed Design Procedure

8.2.4.2.1

TDMCA Mode Determination

The PCM1795 device 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 69 shows the LRCK and BCK timing that determines the TDMCA mode. The PCM1795 device enters

TDMCA mode after two continuous TDMCA frames. Any TDMCA commands can be issued during the next

TDMCA frame after entering TDMCA mode.

Figure 69. LRCK and BCK Timing for Determination of TDMCA Mode

8.2.4.2.2

TDMCA Terminals

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 40. The DO signal has a 3-state output so that it can

be connected directly to other devices.

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