Smart Machine Smart Decision
SIM800C_Hardware_Design_V1.00 27 2014-10-30
1K
5.6K
RXD
TXD
RTS
CTS
GPIO
GPIO
EINT
DTE
(3.3V)
5.6K
5.6K
1K
1K
1K
1K
1K
1K
Module
UART1_TXD
UART1_RXD
UART1_RTS
UART1_CTS
UART1_DTR
UART1_DCD
UART1_RI
GND
GND
Figure 19: Resistor matching circuit
If the voltage of UART is 3V or3.3V, the following reference circuits are recommended:
UART1_TXD
RXD
Module DTE
TXD
UART1_RXD
VDD_EXT
10K
10K
GND
GND
Figure 20 : 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:
VDD_EXT
4.7K
47K
UART1_TXD
4.7K
Module
VDD_EXT
RXD
VDD
DTE
Figure 21: TX level matching circuit
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