I do speed control on dc motor using PWM , I want to control it using two output from the controller. one output for pwm and the other for direction control.
I did this circuit in proteus but the motor speed is very low at high frequencies, I don't know what is the problem

 

Take a look at the switching waveform. You're probably getting incomplete switching at high frequency. You should specify what you mean by "high". What frequency is OK and when does it fall off?

 

frequencies below 1k hz is ok but higher than that slow down the motor in simulation.
I need it to work at 20khz ,24 Vcc

 

And the waveform?

 

the output of ir2112 isnot pulses it is constant. but it gives pulses( max amplitude 5 volt) on th Hi ouput when I increase Vc pin 3 to 20 volt

 

Normally the bottom Mosfet switches on for the whole width time, the upper is switching the required width.
Max.