【正文】 to control the motor excitation is transferred in order as follows: If the requirements of motor reversal, the transmission excitation signal can be reversed. 2 control schemeControl system block diagram is as follows The program uses AT89S51 as the main control device. It is patible with the AT89C51, but also increased the SPI interface and the watchdog module, which not only makes the debugging process bees easy and also more stable. The microcontroller in the program mainly for field signal acquisition and operation of the stepper motor to calculate the direction and speed information. Then sent to the CPLD.CPLD with EPM7128SLC8415, EPM7128 programmable logic device of largescale, for the ALTERA pany39。s MAX7000 family. High impedance, electrically erasable and other characteristics, can be used for the 2500 unit, the working voltage of +5 V. CPLD receives information sent from the microcontroller after converted to the corresponding control signal output to the stepper motor drive. Put the control signal drives the motor windings after the input, to achieve effective control of the motor. The hardware structure of the motor driveMotor drive using the following circuit: R1R8 in which the resistance value of 320Ω. R9R12 resistance value . Q1Q4 as Darlington D401A, Q5Q8 for the S8550. J1, J2 and the stepper motor connected to the sixlead。Advantages and disadvantages of stepper motorAdvantages 1. The motor rotation angle is proportional to the number of pulses。 2. When the motor stopped with a maximum torque (when the winding excitation time)。 3. Since the accuracy of each step in the three per cent to five per cent, and the error will not accumulate to the next step and thus has better positional accuracy and repeatability of movement。 4. Excellent response from the stop and reverse。 5. In the absence of brush, high reliability, it just depends on the life of the motor bearing life。 6. Motor response only determined by the number of input pulses, which can be used open loop control, which makes the motor and control structure can be relatively simpleSystem cost 7. Just load directly connected to the motor shaft can also be extremely slow synchronous rotation. 8. Speed ??is proportional to the pulse frequency, and thus a relatively wide speed range.Shortings1. If not properly controlled prone to resonance。2. Difficult operation to a higher speed.3. Difficult to obtain high torque4. There is no advantage in terms of volume weight, low energy efficiency.5. Over load will destroy the synchronization, the work will be issued when highspeed vibration and noise.Stepper motor drive requirements(1) to provide fast rise and fall of current speed, the current waveform as close as possible rectangle.For the period ended with the release of the loop current flow, to reduce the winding ends of the back electromotive force, to accelerate the current decay.(2) rhyme with higher power and efficiency.Stepper motor driver, which is the control pulse signal emitted into the angular displacement of the stepper motor, or: the control system sends a pulse signal each through the stepper motor drive to rotate a step angle. That is the stepper motor speed is proportional to the frequency and pulse signals. Therefore, the frequency control pulse signal, to be precise motor speed control。 control the number of step pulses to connect the motor accurately. Stepper motor drive there are many, we should take a reasonable choice of power requirements of the drive, the following were introduced various types of typical drive.The latest technological developmentsDomestic and international research on the subdrive technology is very active, highperformance subdriver circuit can be broken down into thousands or even any subdivision. Now able to do plicated calculations to make after the breakdown of uniform step angle, which greatly improves the resolution of stepper motor pulses, reduce or eliminate the vibration, noise and torque ripple, the stepper motor is more class server feature.The actual role of step angle: in the absence of subdrive, the u