Originally Posted by
dcartier
The answer provided, is the best answer.
Because the L298 is expecting to drive the indvidual coils of the stepper, and the Grbl firmware outputs step and direction signals, you need to decode the step and direction signals to feed into the 4 L298 inputs. The easiest way is to use an L297. I just Googled the datasheet and the L297 supports unipolar and bi-polar motors, so no probelm there.
If you want to get more adventurous, you could program a small PIC or AVR to act as the glue logic between the Arduino and the L298.
For the old timers in the group, an up/down counter and a handful of gates could also be used.
If you want it to just work, use the L297.
Dennis