C24 Hardware Interface Manual
Version 0.3
2.8.4 Headset Detection
The module operates by default in the basic audio mode with the handset audio path, for DTMF tones
and speech, and the alert loudspeaker device, for rings and alert tones, active.
The headset path is an alternate audio path in basic mode. It is designed for, but not limited to, a personal
hands-free audio device, a headset, using the headset microphone input device and the speaker output
device. When this path is selected all the audio sounds are passed through to the headset path.
The HDST_INT_N signal is used to switch between handset and headset audio paths in basic audio
mode. This signal is set high by default at power up. Asserting the HDST_INT_N signal low enables the
headset audio path and disables the handset and alert paths. Setting this signal high will disable the
headset path and enable the handset and alert audio paths.
The module supports dynamic switching between the handset and headset audio paths, during operation
and call handling.
The HDST_INT_N signal does not operate in advanced audio mode. This signal’s functionality is
overridden by the AT+MAPATH command settings.
2.8.5 Alert Loudspeaker Port
The alert loudspeaker is the module’s default power-up ringer. It is used for, but not limited to, sounding
the module’s alerts, melodies, and rings. It is located at pins 63 and 65 on the interface connector, named
ALRT_N and ALRT_P respectively.
It is designed with an internal amplifier supplied directly from VCC, which supplies up to 0.5W to the audio
device. It may also be used as a single-ended output referenced to the module’s analog ground.
TABLE 11 – Alert Port Specifications
Parameter Conditions Min
Typ Max Units
Output
No load 2.8 V
PP
Voltage
Gain Programmable in 5dB steps -16 12 dB
AC Output
8 Ω
Impedance
DC voltage VCC/2 V
THD 8Ω load 2 %
Isolation 45 dB
Motorola General Business Use
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