This module can be divided into the following three parts: 
· SCM system: controls the stepping motor; 
* peripheral circuit: PIC microcontroller interface circuit and the stepping motor; 
· the PIC procedures: MCU control interface program stepping power machine, to achieve output triangular wave signal. 
(1) the stepping motor interfaces with the microcontroller. 
SCM is the excellent performance of the control processor, when controlling a stepping motor working, the interface member must have the following functions. 
① voltage isolation. 
Microcontroller operating at 5V, and the stepping motor is working in the tens V, or even higher. Once the voltage of the stepper motor in sequence to the microcontroller, the microcontroller will damage; microcontroller will interfere with the signal of the stepping motor, the system may also lead to errors in the work, so the interface must have a device isolation. 
② messaging function. 
Interface member should be able to convey control information to the stepping motor microcontroller circuit, generates control information necessary for the work, corresponding to different operating modes, the interface member should produce a corresponding operation control waveform. 
③ generate different frequencies required. 
To the stepping motor operate at different speeds to suit different purposes, interface components should produce different operating frequencies. 
(2) the interface voltage isolation. 
Isolation interface isolation voltage dedicated to the low-pressure part of the microcontroller and the stepping motor drive circuit of the high-pressure part, in order to ensure their normal work. 
Voltage isolation pulse transformer interfaces can be used or optical isolator, essentially using optical isolators. The microcontroller output signal can be sent directly to TTL gates or bases of the transistors, the light emitting diode of the photocoupler device and then driven by the transistor.
The light emitting diode of the photocoupler to the internal photodiode device, into an electrical signal, again driving the stepping motor power amplifier circuit, the interface current amplification of the amplifier circuit is a stepping motor preamplifier circuit. Its role is the output signal of the photo isolator amplifies the current, in order to provide sufficient drive current to the amplifier circuit. 
(3) interface to work and the frequency generator. 
MCU controls the stepping motor, the stepping motor needs to be controlled by three I / 0 line at the input and output interface, this time, the microcontroller with RA0 I / O port, RAI, RA2 control of three-phase stepper motor.