so it means I should give 5 v to both the enable pins of the driver.right ?
Yes. Keep 5V on both of the enable pins
and for making half step sequence in my case I will have to use active low logic.right ?
Because you have connected 12V to your common lead on your stepper, your logic will be inverted. So yes. Active low logic.
Or connect the common lead from your stepper to Ground, and use your l293dd to supply 12V. This will allow you to use active high logic.
Nd can u plz tell me what's the difference between stepping freq and pwm freq?
See notes below
For sake of explanation:
PWM is typically used as a digital equivalent to providing an analogue equivalent output to motors and lights. (There are lots of other uses)
When running a motor with PWM, you can control it's speed by changing the PWM's duty cycle. 30% duty cycle is 30% of it's speed. (rough example)
Usually high PWM frequencies are used as it is less noticeable then slower frequencies.
For application with stepper motors, when you want to the motor to 'hold' position, the energy dissipated by the motor increases because the motor is no longer in motion and power is still being applied (otherwise there would be no holding torque). You can help keep the heat down when you want your motor to hold by using PWM. The smaller the duty cycle, the less heat is generated, but the less torque you will have.
Stepping frequency now is how fast you are feeding steps to your stepper motor. The faster your stepping frequency, the faster your motor will turn. (To a point)
Please note that if you want to use PWM while the motor is running, you need to pick a frequency for your PWM that is much higher than the frequency that your providing steps to your motor.
PWM essentially turns on/off your motor very quickly... if it turns off in the middle of a step, your motor will free-wheel until it is turned on again which can result in the chattery noisy result you are getting.
If your PWM is high enough it happens so quickly that even if it turns off while the motor is taking a step, it will turn on again so fast that you won't notice anything.
One more issue with using PWM while turning the motor... Stepper motors usually operate at variable stepping frequencies... if the PWM you are using to keep heat down is a multiple of the stepping frequency you end up with issues do to harmonics that you will not notice unless the motor moves at a specific speed. (This is hard to identify)
For the sake of your project, I would limit the use of PWM to never... or only when you want the motor to stop. (Keep the outputs the same on the microcontroller, and feed PWM to the inputs.)
Just to clarify, in your application, PWM has nothing to do with motor speed, and will only help you manage waste heat as a trade-off for torque.
Stepping frequency has everything to do with speed of the stepper motor
Edit:
Found an extended data sheet... and although the section is for a 297 and
not a 293 look at page 32 (or 5/12) it does have some useful information for driving stepper motors and will show the desired values for the enable pins and the 4 input/outputs. (Note that Stepper motors have a firing order much like cars do... it is important that the order is correct or it will not run well)
