Software Upgrade And Debug; Audio Interfaces - SimCom SIM900B Hardware Design

Autobauding allows SIM900B to automatically detect the baud rate of the host device. Pay more attention to the
following requirements:
Synchronization between DTE and DCE:
When DCE powers on with autobauding enabled, user must firstly send character "A" to synchronize the
baud rate. It is recommended to send "AT" until DTE receives the "OK" response, which means DTE and
DCE are correctly synchronized. For more information please refer to the AT command "AT+IPR".
Restrictions of autobauding operation:
The DTE serial port must be set at 8 data bits, no parity and 1 stop bit.
The URC such as "RDY", "+CFUN: 1" and "+CPIN: READY" will not be reported.
Note: User can use AT command "AT+IPR=x" to set a fixed baud rate and the setting will be saved to non-volatile flash
memory automatically. After the configuration is set as fixed baud rate, the URC such as "RDY", "+CFUN: 1" and "+CPIN:
READY" will be reported when SIM900B is powered on.
Debug port:
Used for debugging and upgrading firmware.
Debug port supports the baud rate of 115200bps.
3.6.2

Software Upgrade and Debug

Refer to the following figure for debugging and upgrading software.
MODULE
DBG_TXD
DBG_RXD
PWRKEY
Figure 17: 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].
3.7

Audio Interfaces

SIM900B 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.
SIM900B_Hardware Design_V2.01
VBAT
VBAT
C1
GND
RS232
TXD_IN TXD_OUT
RXD_OUT RXD_IN
GND
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Smart Machine Smart Decision
PC
RXD
TXD
GND
2012-05-07