[EUnit]

Hi everyone. I'm a complete newbie to this forum thing as far as posting goes but I've got a lot of info from this site in the past few months.

I've started to design a CNC machine from scratch to fit the EMC2 software specifically. I have already made an opto-isolated BOB for parallel interfacing and now I'm working on a Bi-polar stepper driver using Allegro's A3982 stepper driver.

Now I've taken the reprap driver schematic as a starting base but ended altering 95% of the design after I knew what I was doing... HOWEVER I've run into some unsure areas as to what the better option would be.

I included the schematic. First of all my question is about pin 14 ROSC that controls the tOFF. I can't get my thumb on how to figure out what would be a better way to go. Over 3V it defaults to 30us so I can tie it directly to my logic voltage supply or I can connect it to GND with a resistor. But what does this really do? How will it benefit me from one to the other and would it make sense to throw a trim pot in there for fine tuning?

[vger]

The oscilator timing resistor ROSC esentially sets the chopper rate of the driver with about 33.33... KHz (30 usec) being the upper limit. The actual frequency will depend on the current rise-time of the motor coil(s). Setting the oscilator frequency too low could give you erratic results with higher stepping rates.

Steve

[EUnit]

Ok thanks for the reply. It clarifies a few things. I will the just tie that pin straight to my 5v source (as suggested in the Data sheet) and have it default at 30us. Then I wont have to worry about that one anymore