NB-IoT Module Series
BC65 Hardware Design
BC65_Hardware_Design 30 / 55
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.
DTE
VDD_EXT
10 k
Ω
VCC_DTE
4.7 k
Ω
10 k
Ω
VDD_EXT
Module
VDD_EXT
4.7 k
Ω
1 nF
1 nF
RXD
TXD
DBG_TXD
DBG_RXD
AUX_TXD
AUX_RXD
GPIO
GND
GND
DBG_RXD
DBG_TXD
AUX_RXD
AUX_TXD
RI
MAIN_TXD
MAIN_RXD
Figure 18: Reference Circuit with Transistor Circuit
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.
MAIN_TXD
MAIN_RXD
RI
Module
GND
C1+
C1-
C2+
C2-
V+
VCC
GND
V-
3.3 V
T1IN
T2IN
T3IN
T4IN
R1IN
R2IN
R3IN
R1OUT
R2OUT
R3OUT
T1OUT
T2OUT
T5OUT
T3OUT
T4OUT
T5IN
GND
GND
/R1OUT
1
2
3
4
5
7
8
9
GND
To PC Main UART Interface
GND
RS-232
Transceiver
6
Level
Translator
(1.8
–
3.3 V)
Figure 19: Sketch Map for RS-232 Interface Match