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4.6.1 Function of Serial Port
Serial port:
z Full modem device.
z Contains data lines TXD and RXD, hardware flow control lines RTS and CTS, status lines DTR, DCD and
RI.
z Serial port can be used for CSD FAX, GPRS service and AT communication..
z Serial port supports the following baud rates:
1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200bps
z Autobauding only supports the following baud rates:
1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200bps
z The default setting is autobauding.
Autobauding allows SIM808 to automatically detect the baud rate of the host device. Pay more attention to the
following requirements:
z Synchronization between DTE and DCE:
When DCE powers on with autobauding enabled, firstly, user must send character “A” or “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”.
z 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 SIM808 is powered on.
4.6.2 Serial Port
The following figure shows the connection between module and client (DTE).
Figure 22: Connection of the serial port
If the voltage of UART is 3.3V, the following reference circuits are recommended. If the voltage is 3.0V, please
SIM808_Hardware Design_V1.00 2014.03.27
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