Hi Jolip Please learn us how to you do it. I have stepper driver with CW/CCW pins vs STEP/DIR. I would like to modify the GRBL code to use my own stepper's driver. I know that I have to modify the function "ISR(TIMER1_COMPA_vect)" in sprinter.pde, but I dont know how can I do it. Please help me. Thank youby afsharizqi - Firmware - mainstream and related support