Quectel BC66 Hardware Design page 32

The following circuit shows a reference design for the communication between the module and a PC with
standard RS-232 interface. Please make sure the I/O voltage of level shifter which connects to module is
1.8V.
Module
TXD
RI
RXD
GND
Please visit vendors' websites to select a suitable RS-232 transceiver, such as: http://www.exar.com and
http://www.maximintegrated.com.
BC66_Hardware_Design
VDD_EXT
Module
10K
RXD
TXD
VDD_EXT
RXD_DBG
TXD_DBG
RXD_AUX
TXD_AUX
RI
GND
Figure 19: Reference Circuit with Transistor Circuit
C1+
C1-
C2+
C2-
T1IN
T2IN
T3IN
T4IN
Level Shifter
T5IN
(1.8V~3.3V)
/R1OUT
R1OUT
R2OUT
R3OUT
Figure 20: Sketch Map for RS-232 Interface Match
4.7K
VDD_EXT
1nF
1nF
10K
VCC_DTE
4.7K
V+
GND
VCC 3.3V
V-
T2OUT
T1OUT
T5OUT
T3OUT
T4OUT
R1IN
R2IN
R3IN
RS-232
Transceiver
NB-IoT Module Series
BC66 Hardware Design
DTE
TXD
RXD
TXD_DBG
RXD_DBG
TXD_AUX
RXD_AUX
GPIO
GND
GND
GND
GND
To PC Main Serial Port
1
6
2
7
3
8
4
9
5
GND
31 / 59