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

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SIM800L

SIM800HSIM800L_Hardware Design_V2.02 30 2015-07-27 Smart Machine Smart Decision
Figure 21: Resistor matching circuit If the voltage of UART is 3V or3.3V, the following reference circuits are recommended: Figure 22 : Diode isolation circuit
Figure 23: TX level matching circuit SIM800HSIM800L_Hardware Design_V2.02 31 2015-07-27

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 SIM800H&SIM800L is powered on
.

4.5.2
Serial Interfaces

The following figure shows the connection between module and client (DTE).
Figure 20: 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.
SIM800H&SIM800L_Hardware Design_V2.02 30 2015-07-27

Smart Machine Smart Decision
1K
5.6K
RXD
TXD
RTS
CTS
GPIO
GPIO
EINT
DTE
(3.3V)
5.6K
5.6K
1K
1K
1K
1K
1K
1K
Module
TXD
RXD
RTS
CTS
DTR
DCD
RI
GND
GND
Figure 21: Resistor matching circuit
If the voltage of UART is 3V or3.3V, the following reference circuits are recommended:
Figure 22 : Diode isolation circuit
Note: please make sure the minimum of client high limit should be less than 2.8V minus the diode drop.
If the voltage of UART is 5V, the following reference circuits are recommended:
Figure 23: TX level matching circuit
SIM800H&SIM800L_Hardware Design_V2.02 31 2015-07-27

Smart Machine Smart Decision
Figure 24: RX level matching circuit

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