ZHCSHK8B October 2017 – October 2018 TAS2770
The TAS2770 provides one PDM input that can be used for low latency audio playback or sensor aggregation in TDM/I2C mode. Figure 42 below illustrates the double data rate nature of the PDM inputs. Each input has two interleaved PDM channels, one sampled by the rising edge and the other by the falling edge of the clock.
The PDM inputs are sampled by the PDMCK pin, which can be independently configured as either a PDM clock slave input or a PDM clock master output. The PDM_EDGE[1:0] and PDM_SLV[1:0] register bits select the sample clock edge and master/slave mode for each of the two PDM inputs. In master mode the PDMCK pin can disable the clocks (and drive a logic 0) by setting the PDM_GATE[1:0] register bits low. The PDM_CLK[1:0] register bits select which clock is used to sample each PDM input.
When configured as a clock slave, the PDM clock input does not require a specific phase relationship to the system clock (SBCLK in TDM/I2C Mode), but must have an exact frequency relationship to the audio sample rate. This is equivalent to 64/32/16 (~3 MHz) or 128/64/32 (~6 MHz) times a single/double/quadruple speed sample rate. The PDM rate is set by the PDM_RATE1[1:0] register bits.
When the PDMCK pin is configured as a clock master, the TAS2770 will output a 50% duty cycle clock of frequency that is set by the PDM_RATE1[1:0] register bits (64/32/16 or 128/64/32 times a single/double/quadruple speed sample rate).
The PDM_MAP register bit selects which PDM pin is used for audio playback input and which is used for PDM sensor input. The PDM sensor input can be decimated (time aligned with the IV sense) and transmitted on the SDOUT pin when the device is in TDM/I2C mode.
|PDM Input Pin||Register Bit||Value||Capture Edge|
|PDMD||PDM_EDGE|| ||Rising (default)|
|PDM Input Pin||Register Bit||Value||Master/Slave|
|PDMD||PDM_SLV|| ||Slave (default)|
|PDM Input Pin||Register Bit||Value||Clock Source|
| ||PDMCK (default)|
|PDM Clock Pin||Register Bit||Value||Gating|
|PDMCK||PDM_GATE|| ||Gated Off (default)|
|PDM Input Pin||Register Bits||Value||Sample Rate|
|PDMD||PDM_RATE1[1:0]|| ||2.54 - 3.38 MHz (default)|
| ||5.08 - 6.76 MHz|
| ||PDMD pin for sensor input (default)|
| ||PDMD pin for playback|