Specifications

Before running the code, the piggy back board was connected to the Ethernut. The 12
connection are outlined in table 3.
Piggy back
connection
Function Connection on Ethernut
OUTR Audio right channel out. NC
OUTL Audio left channel out NC
DCLK Clock for the data line PORTB PIN 1
DREQ This goes high when the decoder is
running out of data.
PORTE PIN 6
BSYNC This line is used to synchronize
between bytes transferred.
PORTB PIN 5
CS This selects whether the decoder
reads data from the data line or the
command line.
PORTB PIN 4
RESET Resets the decoder. PORTB PIN 7
SCK Clock for the command line PORTB PIN 1
SO Data line out from the decoder. PORTB PIN 3
SI Data line into the decoder PORTB PIN 2
VCCIN Voltage rail in. 5 volts. VCC
GND Ground rail. GND
Table 3 The connections between the Ethernut and the VLSI piggy back board.
From the table you can see that the interface to the decoder is to two data lines, one to
pass commands and configuration data and the other to send the actual MP3 data.
To operate the decoder the user must be able to write to the configuration registers as
well as the data register of the decoder. The operations required to command register are
shown figure 15.
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