AVR ATMega8535, L297, and Stepper Motor

I have a unipolar stepper motor which I would like to drive using L297. The circuit is ready and tested, the result was okay. The thing I need to discuss about here is the CLOCK problem. I tried to give clock input from my ATMega8535 with 4.0Mhz oscillator on board. The result was actually very weird, I need your explanation if any, regarding my issue here:

1. I tried to do simple software PWM, simply bring one output pin to high for 500ms and low for 500ms. The clock input used to increase/decrease the rpm of a stepper motor but when I changed the time on and off, the rpm is the same.

2. I tried with 555 timer a astable/oscillator mode and it operates well with different resistances and capacitance values.

Any idea guys?

Maybe there is something wrong with the code of your Atmel device?

Considering the OPs avatar is the Microchip logo...

blueroomelectronics said:

Considering the OPs avatar is the Microchip logo...

Click to expand...

?? Not sure what you mean

Look under his name, it's a Microchip (PIC) logo. Anyway he'll have to post his code if he want's us to help else it's just guessing.

Hmmm...thought so...He's already proved that his Atmel based unit is at fault by the fact that the simple 555 unit does what he wants and expects....