Example on 8254Motor Control • Stepper motors are used in a wide variety of applications like Floppy Disc, Printer, Plotter(X-Y-Z positioning). • We control the stepper motor using 8254 chip. • Assume we use the frequency of the clock in microprocessor is 8MHz • When the torque on the stepper is negative it will rotate counter clockwise (CCW) and when the torque is positive the stepper will rotate clockwise(CW). • The low signal in the output (Q) is the negative torque , and the high signal is the positive torque
The stepper motor 8MHz to run the 8254 The signal out from CNT0 enter into the PRE The signal out from Q from the JK F-F controls the stepper motor The signal out from CNT1 enter into the CLR
We can’t use 8Mhz to run thestepper motor so, we use thenumber (30,720), then (8MHz/(30,720)=260Hz). 260Hz is small and fit in one byte We use CLR as reference, so What is the mode we used here? We used mode 2, because we have repeated pulses When the signal of preset is coming the stepper will start work,the questions is , it will rotate CW or CCw or what? As we can see the +ve Torque is equal to the –ve torque => the stepper will stop and will not work When the new pulse becomes from CLR the output from Flip-Flop becomes zero Here+ve Torque is greater than the –ve torque =>the stepper motor will move CW Here+ve Torque is less than the –ve torque =>the stepper motor will move CCW
Example on 8254Motor Control • The stepper motor will stop, move CW or move CCW according the width of the output signal, this technique is called Pulse width modulation(PWM).