How do I properly ground an L293D h-bar chip?

[GOT]

I was getting ready to wire up my L293D h-bars and I found that the tutorials I have on the subject are lacking.  I understand using two different power sources, one 5V for the chip and a separate source (12V in my case) for the motor.  The tutorial says "Most motors consume more current than a microprocessor, and need their own supply. The motor and the microcontroller need a common ground, however."  This part confuses me.  If I use the 5V from my Prop 2 I/O pins, I am not going to ground it to my 12V wall wart (or am I?).  The chip has four grounds, one for each half-bar.  Do all four of these ground to the motor power supply?  Do I need to protect the Prop 2 somehow?

[JonnyMac]

Tie the grounds together.
Connect the grounds to the Prop-2 (GND terminal).
You can power the logic side of the L293 with +5 from the Prop-2 (connect to Vcc1 - pin 16)
Connect the positive side of the motor supply to Vcc2 - pin 8
Connect the ground side of the motor supply to the Prop-2 GND terminal

Motors generate a lot of noise which can be upsetting to microcontroller circuits so I suggest completely separate supplies for the Prop-2 and the motors.

[GOT]

Thanks.