Hi
I had a second look at your idea, and i have to say its an interesting one
It should work. I'll have to try this out.
The one thing that will probably kill the driver is when pins 1 and 2 are high.
I would use a logic NOT, something like 4069, so this can never happen
You also have to limit the current to max. of 500mA per output because that's the maximum the driver can sink. You could use 2 outputs parallel to get 1A max. sink capability. But then you can only control one motor with one driver.
Another problem i see is sleep mode and stepping.
To use your schematics, without limiting anything, you would have to use a motor that is not using more then 500mA, which will not give you much power. And power is what you need in any CNC project.
This being a nice and interesting idea, i would still go with a bipolar or unipolar stepper driver that can power motors up to 3A or more. They are easy to implement and have all the needed features like micro stepping, sleep mode, overheat protection and it's all in one chip
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