Once upon a time, I did the lab assignment for this course that involved the technique described in this page. It works. However, a number of us were blowing out our L293Ds. The motor that you describe sounds like it is pushing the absolute maximum ratings. You can expect to destroy L293Ds if you do this; no device was ever intended to operate at its absolute maximum ratings, and I bet you'll find a few threads on 8052.com discussing that matter.


Note that the connection of pins 4/5/12/13 is not an option; they are internally connected, and it is expected that you will connect them in your design as well. The IC has four ground pins configured like this not only to satisfy its current requirements without unacceptable internal ground rise, but also to allow it to help it more effectively dissipate heat into your PCB's ground plane. Unfortunately, the device does not have seperate/isolated logic and drive power supply inputs. If you want your microcontroller isolated from the L293D drive circuitry, it will be up to you to do this using a combination of seperated isolated power supplies and optoisolators.

--Sasha Jevtic