© Semtech 2005 www.semtech.com
9
XE3005/XE3006
2.1.7 Serial Peripheral Interface - SPI
The SPI interface is used to control register values. It is a serial communications interface that is independent of the rest
of the CODEC. It allows the device to communicate synchronously with a microprocessor or DSP. The CODEC interface
only implements a slave controller.
A detailed description can be found in chapter 3.3.
2.1.8 Sandman™ ADC Function
The Sandman™ function monitors the signals, which are processed in the ADC signal channel and the DAC signal
channel. The logic output signal SMAD indicates whether the ADC signal channel has processed an audio signal or only
noise, and for how long. The reference signal amplitude can be selected through register O, the time window parameters
are the off time and on time (registers L, M and N).
Amp.
Σ∆
modulator
Decimator
Serial Audio
Interface
BCLK
FSYNC
SDO
AIN
Sandman
Interface
SMAD
Figure 8: Implementation of the Sandman function for the ADC (SMAD)
The logic output SMAD can be used to power-down or reduce clock speed in other devices in the application, such as a
microcontroller, DSP or wireless link. Also, SMAD can be used as phone pick-up indicator. The Sandman™ function is
illustrated in Figure 9 and is valid for both SMAD (related to the ADC signal) and SMDA (related to the DAC signal).
Initially, SMAD is inactive (low), which means that “noise” is processed by the ADC, i.e. no audio signal amplitude above
the Reference. The Sandman™ Interface compares every output sample of the ADC signal channel to the Reference
value. If the signal is lower than the Reference value, SMAD remains inactive (low).
As soon as the signal passes the reference (time = 1), the on-time counter is started. (for the moment defined by time=’x’
see Figure 9). However, as the signal returns below the reference (time = 2) before the on-time counter has reached the
on time, the on-time counter is reset and the SMAD signal remains inactive (low).
The next time the signal gets higher than the Reference (time = 3), the on-time counter is started again and when it
reaches the on time, the SMAD signal becomes active (high), indicating that an audio signal is present (time = 4). As long
as the signal remains above the Reference, nothing happens and the SMAD signal remains active (high). When the
signal falls below the Reference (time = 5), the off-time counter is started, but as it does not reach the off time before the
signal passes again the Reference (time = 6), SMAD remains active (high). Also during the period from time = 7 to time =
8, the off time counter does not reach the off time.
When the signal falls below the Reference (time = 9) and remains below the Reference until the off-time counter has
reached the off-time, the SMAD signal is changed into the inactive (low) state (time = 10).
