LPWA Module Series
BG77 Hardware Design
BG77_Hardware_Design 41 / 76
Table 15: Logic Levels of Digital I/O
The module provides 1.8V UART interfaces. A level translator should be used if customers’ application is
equipped with a 3.3V UART interface. A level translator TXS0108EPWR provided by
Texas Instruments
is recommended. The following figure shows a reference design of the Main UART interface:
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
0.1uF
0.1uF
RI_MCU
DCD_MCU
RTS_MCU
RXD_MCU
DTR_MCU
CTS_MCU
TXD_MCU
VDD_MCU
Translator
10
K
120K
Figure 17: Reference Circuit with Translator Chip
Please visit http://www.ti.com for more information.
Another example with transistor translation circuit is shown as below. The circuit design of dotted line
section can refer to that of solid line section, in terms of both module input and output circuit designs, but
please pay attention to the direction of connection.
Parameter
Min.
Max.
Unit
V
IL
-0.3
0.6
V
V
IH
1.2
2.0
V
V
OL
0 0.45
V
V
OH
1.35
1.8
V
