Motorola G24 - Digital Audio Interface

Audio Interface
34 Module Hardware Description January 1, 2006
Important: When implementing a single ended loudspeaker design, it is required to place a
series capacitor and resistor on the alert output line, as illustrated in Figure 2-22.
The capacitor should be of low tolerance with values of C = 10-22 uF.
The resistor value should be R = 0
Ω at the design stage, but may be changed to a
different value during audio safety testing, in case attenuation in the speaker gain is
required.
Digital Audio Interface
The G24 digital audio interface is a serial Pulse Code Modulation (PCM) bus, which uses linear
2's compliment coding. G24 is the PCM bus master, supplying the clock and sync signals to the
application.
The G24 digital interface is a 4 signal PCM bus, which includes a bit clock output signal for the
bus timing, a frame sync output signal for audio sampling timing, and serial data input and output
signals.
Important: The PCM bus signals are shared internally by the G24 analog audio interface and
the digital audio interface. Therefore, when using the analog audio interface the
PCM bus signals are active but must not be connected at the interface connector.
The PCM bus is allocated, by default at power up, to the analog audio interface.
Only after switching to digital audio mode, the PCM interface bus may be
connected.
Important: The PCM bus is designed with a break-before-make switching configuration when
transmitting between analog and digital audio modes. Therefore, the hardware
interface connection to the PCM bus signals must be disconnected prior to
switching between audio modes with the AT+MADIGITAL command.
Table 2-9:
Alert Port Specifications
Parameter Conditions Min Typ Max Unit
Output Volt-
age
No load
Single ended
3.5 V
PP
Gain Programmable in
3 dB steps
021dB
AC Output
Impedance
8 Ω
DC Voltage VCC/
2
V
THD 8 Ω load
200 Hz - 20 kHz
0.1 3 %
Isolation 60 dB