Software Upgrade And Debug; Audio Interfaces - SimCom SIM900D Hardware Design

Used for debugging and upgrading firmware.
Debug port supports the baud rate of 115200bps.
4.6.2

Software Upgrade and Debug

Refer to the following figure for debugging and upgrading software.
MODULE
DBG_TXD
DBG_RXD
PWRKEY
Figure 23: Connection for software upgrading and debugging
The serial port and the debug port support the CMOS level. If user connects the module to the computer, the
level shifter should be added between the DCE and DTE.
For details about software upgrading, please refer to document [4].
4.7

Audio Interfaces

SIM900D provides two analog inputs, MIC1P/1N and MIC2P/2N, which could be used for electret microphone.
The module also provides two analog outputs, SPK1P/1N and SPK2P/2N. The output can directly drive 32Ω
receiver.
AT command "AT+CMIC" is used to adjust the input gain level of microphone. AT command "AT+SIDET" is
used to set the side-tone level. In addition, AT command "AT+CLVL" is used to adjust the output gain level. For
more details, please refer to document [1] and document [5].
In order to improve audio performance, the following reference circuits are recommended. The audio signals have
to be layout according to differential signal layout rules as shown in following figures. If user needs to use an
amplifier circuit for audio, National Semiconductor Company's LM4890 is recommended.
SIM900D_Hardware Design_V2.02
VBAT
VBAT
C1
GND
RS232
TXD_IN TXD_OUT
RXD_OUT RXD_IN
GND
31
Smart Machine Smart Decision
PC
RXD
TXD
GND
2012-05-07