If the flyback diode is "really" the wrong way round...

I know a flyback diode goes "backwards", ie cathode to +ve. But what would happen if it's put the right way round (ie, the wrong way round for a flyback), with the anode to +ve.

I'm reluctant to try it: to me that looks like a short across the motor to ground.

Correct.

Paul__B:
Correct.

Supplementary question then… how do they do it in an h-bridge, where “right” and “wrong” depend on the polarity for directional purposes.

edit… I see the 293D datasheet has them like the attached.

hbridge flybacks.PNG

Is there still a question there? The schematic is rather abbreviated, so I'm not certain if you've answered your own question.

In case anyone else is still wondering, in the case of an H bridge, the diodes go across the driver transistors, rather than the motor coils.

Like this: http://forum.arduino.cc/index.php?topic=50931.msg363815#msg363815