Trinamic TMC2100 modes without jumpers

Hello,
I would like to logically order the Trinamic TMC2100 motor driver CFG1 and CFG2 pins (“stealthChop”, “spreadCycle” and “Fullstep” modes)
To do so, it is necessary to change the state of these 2 pins in GND, VCC or OPEN (see datasheet http://reso-nance.org/wiki/_media/projets/zohrawasnotborninaday/tmc2100_datasheet.pdf)

I’ve connected CFG1 on pin 48 of my arduino Mega, and CFG2 on pin 47
While doing research on the web, I came to the conclusion that I could change the state of the pins as follows:
GND: pinmode (pin, OUTPUT), followed by digitalWrite (pin, LOW)
VCC: pinmode (pin, OUTPUT), followed by digitalWrite (pin, HIGH)

OPEN: pinmode (pin, OUTPUT), followed by pinmode (pin, INPUT) (See http://forum.arduino.cc/index.php?topic=12212.0)

Well, it does not work. It seems that whatever I do, the TMC stays in stealthChop mode (the quieter mode)

An idea? Has anyone ever piloted the TMC2100’s modes?