Hi Wayne,

The instructions for the G540 doesn't say you can't have a resistor so I guess you do need one. They are set up for an output current of 1A per kohm of resistance, so I read it as you need a 3.5kohm (3.3k + 220R in series). The limit of 3.5A is the maximum safe working limit for the stepper driver, I suspect it will actually go a little higher than that and if you leave the resistor off it will default to some value just above 3.5A, however that may not be a safe operating mode.