how does the motor shield work?

[zoraster]

I understand how the l293 chips work but where would I find a description of how the 74hc595 works with the l293's. Some where I remember reading that the 595 somehow enabled both of the l293's to work together but I would like to know a little more theory about the board if possible.

[adafruit_support_bill]

There is a nice writeup here: http://docs.google.com/View?docid=dgwf6cmm_2fznx7qgr