Digital Audio Interface - Motorola G24 Developer's Manual

Audio Interface
Important:

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:
Important:
34
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
The capacitor should be of low tolerance with values of C = 10-22 uF.
The resistor value should be R = 0
different value during audio safety testing, in case attenuation in the speaker gain is
required.
Table 2-9: Alert Port Specifications
Parameter Conditions
Output Volt- No load
age Single ended
Gain Programmable in
3 dB steps
AC Output
Impedance
DC Voltage
THD 8 Ω load
200 Hz - 20 kHz
Isolation
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.
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.
Module Hardware Description
at the design stage, but may be changed to a
Ω
Min Typ Max
3.5
0 21
8
VCC/
2
0.1 3
60
Figure 2-22.
Unit
V
PP
dB
Ω
V
%
dB
January 1, 2006