Product Info

LTE Standard Module Series
EC25 Series Hardware Design
EC25_Series_Hardware_Design 52 / 126
The module provides 1.8 V UART interface. A level translator should be used if customers’ 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.
VCCA VCCB
OE
A1
A2
A3
A4
A5
A6
A7
A8
GND
B1
B2
B3
B4
B5
B6
B7
B8
VDD_EXT
RI
DCD
RTS
RXD
DTR
CTS
TXD
51K
51K
0.1 μF
0.1 μF
RI_MCU
DCD_MCU
RTS_MCU
RXD_MCU
DTR_MCU
CTS_MCU
TXD_MCU
VDD_MCU
Translator
10K
120K
Figure 19: Reference Circuit with Translator Chip
Please visit http://www.ti.com for more information.
Another example with transistor translation circuit is shown as below. For the design of circuits shown in
dotted lines, please refer to that shown in solid lines, but please pay attention to the direction of
connection.
MCU/ARM
TXD
RXD
VDD_EXT
10K
VCC_MCU
4.7K
10K
VDD_EXT
TXD
RXD
RTS
CTS
DTR
RI
RTS
CTS
GND
GPIO DCD
Module
GPIO
EINT
VDD_EXT
4.7K
GND
1 nF
1 nF
Figure 20: Reference Circuit with Transistor Circuit
V
IH
1.2
2.0
V
V
OL
0
0.45
V
V
OH
1.35
1.8
V