Smart Machine Smart Decision
SIM800_Hardware Design_V1.10
29
2018-08-13
Note: Hardware flow control is disabled by default. The AT command “AT+IFC=2,2” can enable hardware
flow control .The AT command “AT+IFC=0,0”can disable hardware flow control. For more details, please
refer to document [1].
Table 9: Serial port characteristics
Symbol
Min
Max
Unit
V
IL
-0.3
0.7
V
V
IH
2.1
3.0
V
V
OL
-
0.4
V
V
OH
2.4
-
V
4.5.1
Function of Serial Port
Serial port:
Full modem device.
Contains data lines TXD and RXD, hardware flow control lines RTS and CTS, status lines DTR, DCD and
RI.
Serial port can be used for CSD FAX, GPRS service and AT communication. It can also be used for
multiplex function. For details about multiplex function, please refer to
table 11
.
Serial port supports the following baud rates:
1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200bps, 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 SIM800 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, 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”.
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 SIM800 is powered on.
4.5.2
Serial Port
The following figure shows the connection between module and client (DTE).
