SimCom SIM7020E - UART Interface; UART Design Guide

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SIM7020_Hardware_Design_V1.02 21 2018-07-25
3.5 UART Interface
SIM7020 provides a 7-wire UART1 (universal asynchronous serial transmission) interface as DCE
(Data Communication Equipment). AT commands and data transmission can be performed through
UART1 interface.UART2 can be used for debugging and download software.
3.5.1 UART Design Guide
The following figures show the reference design.
TXD
RXD
RTS
CTS
UART _DTR
UART _ DCD
UART1_RI
TXD
RXD
RTS
CTS
DTR
DCD
RING
MODULE (DCE)
CUSTOMER (DTE)
Serial portSerial port
Figure 10: UART full modem
MODULE
( DCE)
HOST
( DTE)
UARTUART
TXD
RXD
RTS
CTS
DTR
DCD
RI
TXD
RXD
RTS
CTS
DTR
DCD
RING
Interrupt
Wake up host
Figure 11: UART null modem
The SIM7020 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.