Figure 12: Reference Circuit Of Level Shift - SimCom SIM7020C Hardware Design

MODULE
UART
Note: When it uses the level shifter IC, the pullupresistance on TXD_3.3V
DCD_3.3V should not be less than 47KΩ.
Also the following reference circuit is recommended:
GSM
VDD_EXT
UART1_TXD
GSM
VDD_EXT
UART1_RXD
Note: The default band rate is 115200bps. The triode conversion circuit is not suitable for high
band rate more than 460800. When using UART2 for downloading software, the band rate is
921600bps, please pay attention to the device's speed support.
SIM7020_Hardware_Design_V1.02
VDD _ EXT
100nF
TXD
RXD
RTS
CTS
DTR
DCD
RI
47K

Figure 12: Reference circuit of level shift

VDD_EXT
4.7K
47K
Figure 13: TX level matching circuit
VDD_EXT
4.7K
Figure 14: RX level matching circuit
3.3V
TXB0108 RGYR
VCCA VCCB
OE
GND
B1
A1
A2 B2
A3 B3
B4
A4
B5
A5
B6
A6
A7 B7
47K
B8
A8
VDD
4.7K
RXD
VDD
4.7K
47K
TXD
22
Smart Machine Smart Decision
100nF
TXD _3.3V
RXD _3.3V
RTS _3.3V
CTS _3.3V
DTR _3.3V
DCD _3.3V
RI_3.3V
DTE
DTE
2018-07-25
， ，RTS_ 3.3V