Product Info

NB-IoT Module Series
BC660K-GL Hardware Design
BC660K-GL_Hardware_Design
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Figure 14: Sketch Map for RS-232 Interface Match
Please visit vendors’ websites to select a suitable RS-232 transceiver, such as: http://www.exar.com and
http://www.maximintegrated.com.
1. If the voltage domain of your application system is 1.8 V, keep the R1 marked in red not mounted; If
the voltage domain of your application system is 3.3 V, keep the R1 marked in red mounted.
2. “ ” represents the test points of UART interfaces. It is also recommended to reserve the test points
of VBAT, BOOT and RESET_N, for convenient firmware upgrade and debugging when necessary.
3. VDD_EXT cannot pull up the module MAIN_RXD directly. If VDD_EXT need pull up the module
MAIN_RXD, you need to connect a Schottky diode in series first, and then pull up the module
MAIN_RXD through a 4.7-20 kΩ resistor. For more details, see document [3].
4. When VIO_SEL is grounded and VBAT ˂ 3.3 V, VDD_EXT = VBAT;
When VIO_SEL is grounded and VBAT ≥ 3.3 V, VDD_EXT = 3.3 V;
When VIO_SEL is floating, VDD_EXT = 1.8 V.
When the serial port voltage is neither 1.8 V nor 3.3 V, it is recommended to use a transistor level
conversion circuit. The circuit design of dotted line section can refer to the design of solid line section, in
terms of both module input and output circuit designs, but please pay attention to the direction of
connection.
NOTES