Cheap Chinese TB6600 with Marlin

Hey Reprap community,

So, I've bought these cheap chinese TB6600.
They have a Toshiba Stepper driver chip S109AFTG.
It's actually a pretty good chip. Not fully implemented in the design, but it will do.
There are options for Motor Ach current sense and Motor Ach output that are not used.
However, there is 1 major issue with this.
For turning the stepper motor clockwise or counter clockwise,
there are 2 Dir ports. Dir- and Dir+
The sequence to make it run clockwise is Dir- = Low and Dir+ = High.
for the counter clockwise, this is Dir- = High and Dir+ = Low.

So the 1 DIR pin on a RAMPS is not enough to use it.
We don't need the reset or sleep pin from the RAMPS board.
But Marlin is not configured for this. And I'm not sure where to place the piece of source code for this.
Any care to help me out here ???

kind regards,
Thierry