Datasheet
Data Sheet AD1974
Rev. D | Page 13 of 24
TDM MODES
The AD1974 serial ports also have several different TDM serial
data modes. The first and most commonly used configuration
is shown in Figure 6 where the ADC serial port outputs one
data stream consisting of four on-chip ADCs followed by four
unused slots. In this mode, ABCLK is set to 256 f
S
(8-channel
TDM mode).
The I/O pins of the serial ports are defined according to the
serial mode selected. For a detailed description of the function
of each pin in TDM and AUX Modes, see Table 12.
The AD1974 allows system configurations with more than four
ADC channels (see Figure 7 and Figure 8) that use 8 ADCs and
16 ADCs. In this mode, four AUX channel slots in the TDM out-
put stream follow four on-chip ADC channel slots. It should be
noted that due to the high ABCLK frequency, this mode is
available only in the 48 kHz/44.1 kHz/32 kHz sample rate.
SLOT 1
LEFT 1
SLOT 2
RIGHT 1
SLOT 3
LEFT 2
SLOT 4
RIGHT 2
MSB MSB–1 MSB–2 ADATA
ABCLK
ALRCLK
UNUSED UNUSED UNUSED UNUSED
A
LRCLK
ABCLK
ADATA
256 BCLKs
32 BCLKs
06614-016
Figure 6. ADC TDM (8-Channel I
2
S Mode)
Table 12. Pin Function Changes in TDM and AUX Modes
Pin Name Stereo Mode TDM Mode AUX Mode
ASDATA1 ADC1 data output ADC TDM data output ADCTDM data output
ASDATA2 ADC2 data output ADC TDM data input Not used (float)
AUXDATA1 Not used (ground) Not used (ground) AUXDATA in 1 (from external ADC1)
AUXDATA2 Not used (ground) Not used (ground) AUXDATA in 2 (from external ADC2)
ALRCLK ADC LRCLK input/output ADC TDM frame sync input/output ADCTDM frame sync input/output
ABCLK ADC BCLK input/output ADC TDM BCLK input/output ADCTDM BCLK input/output
AUXLRCLK Not used (ground) Not used (ground) AUXLRCLK input/output
AUXBCLK Not used (ground) Not used (ground) AUXBCLK input/output
ABCLK
ALRCLK
AUXLRCLK
(AUX PORT)
ASDATA1
(TDM_OUT)
AUXBCLK
(AUX PORT)
AUXDATA1
(AUX1_IN)
AUXDATA2
(AUX2_IN)
ADCL1 ADCR1 ADCL2 ADCR2 AUXL1 AUXR1 AUXL2 AUXR2
FOUR-ON-CHIP DAC CHANNELS
32 BITS
LEFT RIGHT
MSB
MSB MSB
MSB MSB
FOUR-AUX ADC CHANNELS
06614-050
Figure 7. 8-Channel AUX ADC Mode