User's Manual

DRAFT
4: VAM-CM interfaces
Pin Signal In/Out Description
#33 dig_Au_Dr In Data in
#37 GND GND
Table 7. Digital audio interface pins
4.2.5.1:Voltage levels
The Digital audio bus is equipped with level shifter in the VAM-CM board. This solution enables VAM
to adjust I/O voltage system by applying own V_io voltage to VAM control interface connector.
Voltage requirements for logic levels are shown in Table 2 . For more details, see Power Supply
interface description on page 16.
4.2.5.2:Data formats
Two modes are available for the PCM protocol: mode 1 and mode 2. For both modes, there are two
types of operation: mono and stereo channels. The difference between PCM mode 1 and PCM mode
2 is in the way they use either the rising or the falling edge of the clock signal, and the frame-
synchronization polarity.
> PCM Mode 1: Input data is latched on the falling edge of the clock, and the transmitted data
starts on the rising edge of the clock. Frame-synchronization pulse is active high.
> PCM Mode 2: Input data is latched on the falling edge of the clock, and the transmitted data
starts on the falling edge of the clock. Frame-synchronization pulse is active low.
Figure 7 and Figure 8 shows an example of PCM protocol, mode 1 and mode 2, respectively, for a
frame composed one word (width: 32 bits) with 16 bits data.
More detailed information concerning PCM interface can be found in Texas Instruments DM3725
documentation .
Figure 7. PCM Protocol – Mode 1 Data Format
15:GSPS Core Module 2.0 VAM-CM HW Description
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