Bidirectional DC motor control interface circuit

Shown is a bidirectional DC motor control interface circuit that implements a reversible pulse width speed regulation PWM system
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    In the figure, the ports PAO and PA1 of 8255 control 4 photoelectric isolators and 4 high-power field effect transistor switches S1-S4 through
the tri-state gate 74LS125 and the inverting 1 driver 7406 .     When PAO-O, PAl=l, the three-state gate G2 in the register 741.S125 is gated, the input stage of the photoelectric isolator LE4 is turned on and emits light, and the output of the phototransistor is high level, so the high-power field The effect transistor switch S4 is turned on. In the same way, the output of 74LS125 tri -state gate 04 is "0", making the control port of tri-state gate G3 at O ​​level. Therefore, tri-state gate G3 is turned off, causing the input level of photoelectric isolator LE1 to emit light and conduct remote control. Thus making sl conductive. Based on the same analysis, it can be seen that S2 and S3 are turned off at this time . Therefore, current flows through the DC motor in the forward direction and the motor rotates. According to the above analysis method, it can also be seen that when PA0 leads to 1. When PAl=O. S2 and S3 are turned on, Sl and S4 are turned off, the current flows through the DC motor in the reverse direction, and the motor reverses. When PAO -1, PAl-1, S2 and S4 are turned on. -Sl and S3 are turned off, and the straight comb motor brakes=l. When PAO-O, PAl=0, S1~S4 are all turned off, and the motor slides freely. ． 1 J i.   In order to realize PWM dispatch of DC motor, after determining the operation mode of the electric mechanism, by controlling the power on and coasting time of the motor (that is, changing the duty cycle), the control of the DC motor can be achieved. The purpose of speed regulation.