SimCom SIM800C Hardware Design page 26

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, the following reference circuits are recommended:
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:
SIM800C_Hardware_Design_V1.02
M odul e(D C E )
S eri al P ort
U A R T1_T X D
U A R T1_R X D
U A R T1_R T S
U A R T1_C T S
U A R T1_D T R
U A R T1_D C D
U A R T1_R I
G N D
Figure 18: Connection of the serial interfaces
U A R T 1_T X D
U A R T 1_R X D
U A R T1_R T S
U A R T1_C T S
U A R T 1_D T R
U A R T1_D C D
U A R T1_R I
5.6K
G N D 5.6K
M odul e
Figure 19: Resistor matching circuit
10K
V D D _E X T
U A R T 1_R X D
U A R T 1_T X D
G N D
M odul e
Figure 20 : Diode isolation circuit
C ust om er(D T E )
S eri al P ort
T X D
R X D
R T S
C T S
D T R
D C D
R I N G
G N D
1K
R X D
1K
T X D
1K
R T S
1K
C T S
1K
G P I O
1K
G P I O
1K
E I N T
G N D
5.6K
D T E
(3. 3V )
T X D
R X D
10K
G N D
D T E
26
Smart Machine Smart Decision
2015-4-27