NI Digital System Development Board User Manual
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© National Instruments
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The audio codec needs to be clocked from the Zynq on the MCLK pin. This master clock will
be used by the audio codec to establish the audio sampling frequency. This clock is required to
be an integer multiple of the desired sampling rate. The default settings require a master clock
of 12.288 MHz, resulting in a 48 kHz sampling rate. For other frequencies and their respective
configuration parameters, consult the SSM2603 datasheet.
The codec has two modes: master and slave, with the slave being default. In this mode, the
direction of the signals is specified in Table 25. When configured as master, the direction of
BCLK, PBLRC and RECLRC is inverted. In this mode, the codec generates the proper
frequencies for these clocks. Digilent recommends that the audio codec be used in slave mode,
because this tends to simplify the clocking scheme of the FPGA logic. No matter where the
clocks are generated, PBDAT needs to be driven out and RECDAT sampled in sync with them.
The master clock is always driven out of the Zynq.
The timing diagram of an I²S stream can be seen on Figure 19. Note the one-cycle delay of the
data stream with respect to the left/right clock changing state. Audio samples are transmitted
MSB first, noted as 1 in the diagram.
Figure 19.
I²S Timing Diagram
The digital mute signal (MUTE) is active-low, with a pull-down resistor. This means that when
not used in the design, it will stay low and the analog outputs of the codec will stay muted. To
enable the analog outputs, drive this signal high. It is important to note that the audio codec will
not receive or transmit any audio data until the MUTE signal is driven high.
To use the audio codec in a design with non-default settings, it needs to be configured over I2C.
The audio path needs to be established by configuring the (de)multiplexers and amplifiers in the
codec. Some digital processing can also be done in the codec. Configuration is read out and
written by accessing the register map via I2C transfers. The register map is described in the
SSM2603 datasheet.
Reset Sources
Power-on Reset
The Zynq supports an external power-on reset signal. The power-on reset is the master reset of
the entire chip. This signal resets every register in the device capable of being reset. The DSDB
uses this signal to hold the Zynq in reset until all power supplies are stable. The user can also
assert the Zynq power-on reset by pressing the red button labeled “PS-PORB”. This (or a power
cycle) is necessary whenever the boot mode is changed using SW8.