Xircom An Intel Company GEM3501 User Manual
Core Engine GSM/GPRS Modem Developer Guide Preliminary Draft: 7/6/2001
29
Part Number: 07100026, Revision: 002
Confidential
© 2001 Xircom, Inc., an Intel company All rights reserved.
All trademarks and copyrights are the property of Xircom, Inc., an Intel company
All trademarks and copyrights are the property of Xircom, Inc., an Intel company
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The Core Engine includes two (2) audio interfaces, each with support for one (1)
microphone and one (1) speaker.
microphone and one (1) speaker.
7.1 Audio Path Selection
Selection of which mic/speaker pair should be active is achieved either by hardware,
using a designated signal on the Core Engine I/O connector, or by software, using an AT
command.
using a designated signal on the Core Engine I/O connector, or by software, using an AT
command.
7.1.1 Hardware Selection of Audio Path
The AUDIO_SEL signal on the (pin 34 of the Core Engine I/O interface) can be used to
select whether the Primary or Secondary mic/speaker should be active.
select whether the Primary or Secondary mic/speaker should be active.
7.1.2 Software Selection of Audio Path
The “AT+SPEAKER” software command can be used to select whether the Primary or
Secondary mic/speaker should be active.
Secondary mic/speaker should be active.
NOTE: Refer to the Core Engine Programmer Reference documentation for the syntax
of how to use this software command.
of how to use this software command.
7.2 Microphone Input
The Core Engine microphone (input) interface specification is shown in Table 8:
Input voltage differential
1.03Vpp
Differential input resistance
50Kohm
Input capacitance
5pF
Table 7: Core Engine microphone interface specification.
Each microphone circuit should have its own RC filtering on the bias supply. Microphone
characteristics vary and exact biasing values may need some experimentation. The
microphone inputs are multiplexed (not summed) into the voiceband receive circuit.
characteristics vary and exact biasing values may need some experimentation. The
microphone inputs are multiplexed (not summed) into the voiceband receive circuit.