Cirrus Logic CS8422 - Manual (Page 27)

DS692F2 27
CS8422
5.1.5 Time Division Multiplexing (TDM) Mode
TDM Mode allows several TDM-compatible devices to be serially connected together allowing their cor-
responding serial output data to be multiplexed onto one line for input into a DSP or other TDM capable
input device.
In TDM Mode, the TDM_IN pin is used to input TDM-formatted data while the SDOUT1 or SDOUT2 (Soft-
ware Mode only) pin is used to output TDM data. If the CS8422 is the first TDM device in the chain, it
should have its TDM_IN connected to GND. Data is transmitted from SDOUTx (SDOUT1 or SDOUT2)
most significant bit first on the first falling OSCLKx edge after an OLRCKx rising edge and is valid on the
rising edge of OSCLKx.
5.1.5.1 TDM Master Mode
In TDM master mode, OSCLKx frequency is fixed at 256*OLRCKx (where x = 1 or x = 2 depending on
which serial output port is selected as being in TDM Mode). Each sample time slot is 32 bit-clock periods
long; providing 8 channels of digital audio multiplexed together, with the first two channels being supplied
by the CS8422 which has been placed in master mode. An OSCLKx-wide OLRCKx pulse identifies the
start of a new frame, with the valid data sample beginning one OSCLKx after the OLRCKx rising edge. In
TDM master mode, the master clock source for the TDM serial port must be 256, 512, or 1024*Fso. Valid
data lengths are 16, 18, 20, or 24 bits.
Figure 13 shows the interface format for TDM master mode. In
TDM master mode, the TDM_IN pin is not supported. Thus the CS8422 placed in TDM master mode
should be the first TDM device in the chain, as shown in
Figure 16
5.1.5.2 TDM Slave Mode
In TDM slave mode, the number of channels that can by multiplexed to one serial data line depends on
the output sample rate. For slave mode, OSCLKx must operate at N*64*Fso, where N is the number of
CS8422’s in the TDM chain. For example, if Fso = 96 kHz, N = 4 (8 channels of serial audio data),
OSCLKx frequency must be 24.576 MHz. Note that the maximum OSCLKx frequency in slave mode is a
function of the VL supply voltage, as shown in
“Switching Specifications” on page 17 . Figure 14 shows
the interface format for TDM slave mode.
5.1.5.3 Hardware Mode Control
In Hardware Mode, TDM Mode is selected through the SAOF pin. See Section 8.1 on page 41 for more
details.
5.1.5.4 Software Mode Control
In Software Mode, TDM Mode is selected through the Serial Audio Output Data Format - SDOUT1 (0Ch)
register, found on page 55 .