Hello Liang,
只有HDMI 显示器插上时，HDMI才会输出信号。HDMI driver会检测HPD信号，确定是否有显示器插进来。
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Only when HDMI screen is connected, HDMI line will output signals to screen. HDMI driver will detect if HDMI cable is plugged in, if yes, signals will be output, otherwise, no signals.
Have a nice day!
TIC weidong sun
