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Another example with transistor translation circuit is shown as below. For the design of circuits shown in
dotted lines, see that shown in solid lines, but pay attention to the direction of connection.
Module
MAIN_RXD
MAIN_TXD
DBG_RXD
DBG_TXD
AUX_RXD
AUX_TXD
The following circuit shows a reference design for the communication between the module and a PC with
standard RS-232 transceiver. Make sure the I/O voltage of level translator which is connected to the
module is 1.8 V.
Module
MAIN_TXD
RI
MAIN_RXD
GND
BC65_Hardware_Design
VDD_EXT
10 kΩ
VDD_EXT
RI
GND
Figure 18: Reference Circuit with Transistor Circuit
C1+
C1-
C2+
C2-
T1IN
T2IN
T3IN
T4IN
Level
Translator
T5IN
–
(1.8
3.3 V)
/R1OUT
R1OUT
R2OUT
R3OUT
Transceiver
Figure 19: Sketch Map for RS-232 Interface Match
4.7 kΩ
VDD_EXT
1 nF
1 nF
10 kΩ
VCC_DTE
4.7 kΩ
V+
GND
VCC
3.3 V
V-
T2OUT
T1OUT
T5OUT
T3OUT
T4OUT
R1IN
R2IN
R3IN
RS-232
NB-IoT Module Series
BC65 Hardware Design
DTE
TXD
RXD
DBG_TXD
DBG_RXD
AUX_TXD
AUX_RXD
GPIO
GND
GND
GND
GND
To PC Main UART Interface
1
6
2
7
3
8
4
9
5
GND
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