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SIM800C_Hardware_Design_V1.00 26 2014-10-30
Serial port can be used for CSD,GPRS service and AT communication. It can also be used for multiplexing
function. For details about multiplexing function, please refer to table 11.
Serial port supports the following baud rates:
1200, 2400, 4800, 9600, 19200, 38400, 57600,115200,230400 and 460800bps
Autobauding only supports the following baud rates:
1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200bps
The default setting is autobauding.
Autobauding allows SIM800C 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, it is recommended to send "AT" or "at" or "aT" or "At"
to synchronize the baud rate, until DTE receives the "OK" response, which means DTE and DCE are
correctly synchronized. For more information please refer to 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: Customer 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 SIM800C is powered on.
4.5.2 Serial Interfaces
The following figure shows the connection between module and client (DTE).
UART1_TXD
UART1_RXD
UART1_RTS
UART1_CTS
UART1_DTR
UART1_DCD
UART1_RI
TXD
RXD
RTS
CTS
DTR
DCD
RING
Serial Port
Serial Port
Module(DCE)
Customer(DTE)
GND GND
Figure 18: Connection of the serial interfaces
If the voltage of UART is 3.3V, the following reference circuits are recommended. If the voltage is 3.0V, please
change the resistors in the following figure from 5.6K to 14K.
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