User's Manual

Smart Machine Smart Decision
SIM7020G_User Manual_V1.00 27 2019-01-15
The SIM7020G UART is 1.8V voltage interface. If user’s UART application circuit is 3.3V voltage
interface, the level shifter circuits should be used for voltage matching. The TXB0108RGYR
provided by Texas Instruments is recommended. The following figure shows the voltage matching
reference design.
TXD
RXD
RTS
CTS
DTR
DCD
RI
A7
A1
A2
A3
A4
A5
A6
MODULE
DCE
TXB0108 RGYR
UART
A8
B7
B1
B2
B3
B4
B5
B6
B8
VCCA
OE
VDD_EXT
VCCB
47K
47K
TXD_3.3V
DTE
3.3V
100nF
100nF
RXD_3.3V
RTS_3.3V
CTS_3.3V
DTR_3.3V
DCD_3.3V
RI_3.3V
Figure 14: Reference circuit of level shift
Note: When it uses the level shifter IC, the pull up resistance on TXD_3.3V, RTS_3.3V, DCD_3.3V
should not be less than 47KΩ.
Also the following reference circuit is recommended:
VDD_EXT
4.7K
47K
UART1_TXD
4.7K
MODULE
DCE
VDD_EXT
RXD
VDD
DTE
Figure 15: TX level matching circuit