SimCom SIM800 Hardware Design page 30

Module(DCE)
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.
If the voltage of UART is 3V or3.3V, user also can use following reference circuits:
SIM800_Hardware Design_V1.10
Serial Port
UART1_TXD
UART1_RXD
UART1_RTS
UART1_CTS
UART1_DTR
UART1_DCD
UART1_RI
GND
Figure 19: Connection of the serial port
UART1_TXD
UART1_RXD
UART1_RTS
UART1_CTS
UART1_DTR
UART1_DCD
UART1_RI
GND
5.6K
Module
Figure 20: Level converting by resistor
10K
VDD_EXT
UART1_RXD
UART1_TXD
GND
Module
Figure 21: Isolation circuit by diodes
30
Customer(DTE)
Serial Port
TXD
RXD
RTS
CTS
DTR
DCD
RING
GND
1K
RXD
1K
TXD
1K
RTS
1K
CTS
1K
GPIO
1K
GPIO
1K
EINT
GND
5.6K 5.6K
TXD
RXD
10K
GND
DTE
Smart Machine Smart Decision
DTE
(3.3V)
2018-08-13