Quectel EG915U-EU Manual page 48

MAIN_DCD
MAIN_TXD
MAIN_RI
MAIN_DTR
AUX_TXD
AUX_RXD
DBG_RxD
DBG_TxD
The module provides 1.8 V UART interfaces. A level translator should be used if the application is
equipped with a 3.3 V UART interface. A level translator TXS0108EPWR provided by Texas Instruments
is recommended. The following figure shows a reference design.
VDD_EXT
0.1 μF
MAIN_RI
MAIN_DCD
MAIN_CTS
MAIN_RTS
MAIN_DTR
MAIN_TXD
MAIN_RXD
Please visit http://www.ti.com for more information.
Another example with transistor translation circuit is shown as below. For the design of circuits in dotted
lines, please refer to that of the circuits in solid lines, but please pay attention to the direction of
connection.
EG915U-EU_Hardware_Design
38 DO
35 DO
39 DO
30 DI
27 DO
28 DI
22 DI
23 DO
VCCA
120K
OE
A1
A2
Translator
A3
A4
A5
A6
A7
51K
A8
Figure 23: Reference Circuit with Translator Chip
Main UART data carrier detect
Main UART transmit
Main UART ring indication
Main UART data terminal ready
Auxiliary UART transmit
Auxiliary UART receive
Debug UART transmit
Debug UART receive
VCCB
0.1 μF
GND
B1
B2
B3
CTS_MCU
B4
RTS_MCU
B5
DTR_MCU
B6
RXD_MCU
B7
TXD_MCU
51K
B8
LTE Standard Module Series
1.8 V power domain.
If unused, keep it
open.
VDD_MCU
RI_MCU
DCD_MCU
Connect the MCU CTS pin
Connect the MCU RTS pin
Connect the MCU RXD pin
Connect the MCU TXD pin
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