Motorola 8900 - Blackberry Curve Cell Phone OEM Car Charger, Developer'S Manual

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Chapter 2: Hardware Interface Description
December 15, 2008 C24 Module Hardware Description 31
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 2-20 .
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 that alert level limitation is
required.
Digital Audio Interface
The C24 digital audio interface is a serial Pulse Code Modulation (PCM) bus, which uses linear
2's compliment coding. C24 is the PCM bus master, supplying the clock and sync signals to the
application.
The C24 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.
The PCM bus signal's configuration is:
•
PCM_CLK - 2048 kHz serial clock
•
PCM_FS - 8 kHz bit-wide frame-sync
•
PCM_DOUT - 13-bit linear audio data output
•
PCM_DIN - 13-bit linear audio data input
The analog audio is sampled at an 8 kHz rate and converted to linear 13-bit serial PCM audio
data. The serial data is transferred on the PCM bus in 16-bit word format, which includes 13
sampled data bits, and 3 added zero value bits.
The 16-bit serial data is transferred in both directions after each sync signal's falling edge. The
sync signal pulse duration is one clock period, after which the serial data is transferred in both
directions for 16 consecutive clock periods.
Following the 16-bit data transfer, the serial input and output data signals inactivate until the next
sync pulse, which occurs every 125 µS (8 kHz). It is recommended the serial data signals will be
High-Z during the inactive period.
Table 2-9: Alert Port Specifications
Parameter Conditions Min Typ Max Unit
Output Volt-
age No load VCC V
pp
Gain Programmable by
AT Command 0 21 dB
AC Output
Impedance 8 Ω
DC Voltage VCC/
2 V
THD 8 Ω load 2 %