User's Manual

HF-A21-SMT Embedded WiFi Module User Manual
Shanghai High-Flying Electronics Technology Co., Ltd
www.hi-flying.com
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Figure 10. Ethernet Reference Design without Transformer
1.3.3. UART Interface
UART interface is the serial data transmition interface mainly used for HF-A21-SMT modules.
User can add RS-232 chipset on user board and convert the signal to RS-232 voltage to
communicate with outside equipment or sensors. HF-A21-SMT modules UART interface include
4 general signals: TXD/RXD/RTS/CTS. The hardware reference design with RS-232 chipset as
following:
Figure 11. UART Interface Reference Design
Notes: TXD pin is also hardware configuration pin internal module. So this pin MUST pull-down
during module power up. HF0A11x modules provide internal pull-down resister, user can‟t add
pull-up/pull-down resister on user board, which may cause module can‟t work.
1.3.4. Power Interface
HF-A21-SMT module support single +3.3V power supply. The peak current shall about 350mA
and normal WiFi working current shall about 200mA. The power save (WiFi OFF) mode will about
100mA
Decoupling at power pin suggested, At least one 100uF and one 10uF capacitor required at user
board and put near module power input pin will increase the reliability and performance.