Microstepping with 16F877A and CCS C

[probus]

Hello Dear All,

I have a unipolar 5V stepper motor and I want to drive it with a 16f877a.
I have connected 2 pieces of tc4427 mosfet drivers and 4 pieces of IRF2807 to the pic and, as I see they are working properly.

I supply 50V to the motor and I am trying to use microstepping techniques. Because the motor is 5V, pwm output of the pic never exceeds 10%.

My schema is same with the schema in this document (http://ww1.microchip.com/downloads/en/AppNotes/00907a.pdf page 19, figure 23) (plus mosfet drivers).

My problem is that, I can only drive the motor very slowly. When I trying to increase the speed, motor is just vibrating.

Here is my some code parts:
Code:
int msTable[] = {0, 2, 4, 6, 7, 8, 9, 10, 8, 6, 4, 3, 2, 1}; //Microstepping look up table


Code:
setup_timer_2(T2_DIV_BY_1,101,1); //49.02 khz


Code:
void takeStep(unsigned int16 stepCount){
static int iCcp1 = 7;
static int iCcp2 = 0;
static int16 i;
static int1 swCcp1 = true;
static int1 swCcp2 = true;

for(i = 0; i < stepCount; i++){

set_pwm1_duty(msTable[iCcp1++]);
if(swCcp1) output_high(PIN_CCP1_SW); else output_low(PIN_CCP1_SW);
set_pwm2_duty(msTable[iCcp2++]);
if(swCcp2) output_high(PIN_CCP2_SW); else output_low(PIN_CCP2_SW);

if(iCcp1 > MAX_MS_TABLE_INDEX){
iCcp1 = 0;
swCcp1 = !swCcp1;
} else if(iCcp2 > MAX_MS_TABLE_INDEX){
iCcp2 = 0;
swCcp2 = !swCcp2;
}

delay_us(1000);
}

}


I am regulating speed by changing the sleep time. Sleep time 1000 and above works fine(but very slowly). When I decrease it, motor is starting to vibrate.

Here is some details of the motor:

3A, 1,66ohm, 7.5mH, nema 24, unipolar.

I have just checked the circuit with a oscilloscope. It works fine at high and low speed.

Please help me :/