STC片四路软件PWM+双路硬件PWM输出程序，串口控制占空比，可直带SG90。软件PWM超高精度。 配套上位机程序，可同时带485连接的多套控制板。-STC-chip four software PWM+ Dual hardware PWM output procedures, serial control duty cycle can be straight with SG90. Ultra-high-precision software PWM. PC matching procedu