Mount 360 degree rotator with camera using 2 pins (Power line and Gnd)

I am designing a rotator circuit which consists of a 5v stepper motor and 5v DRV8834 driver IC. The driver IC got 1 pins which is a step to control the motor. The problem/question is that only a two lines come from the camera top section(combined 12Vpower/5V step line and ground. The camera top section runs at 12V. Is that possible to use the same 12V line to toggle as a 5V step pulse as well? The idea is as soon as the bottom section is connected to the top section, the Intelligent circuit should recognize whether the rotator is receiving 12V power or 5V step signal. If it is 12V then the system stays on and shouldn't consume current as well as doesn't harm the motor. When it receives 5V step signal it goes through the 5V buck regulator (only if needed?) and supply the voltage to the motor and turns on the rotator. Is that possible to connect? I have attached the rough block diagram. Could you please help me?

Thanks in advance.

My first inclination is to use a comparator If the voltage is above, say, 5.5 V then you know that you are receiving 12V power, otherwise you are getting a step signal. To prevent from getting a step signal when power is off, you need another comparator to check that it is above, say, 4.5V. then you use the result to power the motor only when the voltage fits in the 5V range. Of course, I'm assuming that you want the motor to run continuously only when the signal is 5V.

This solution may have problems when you are powering on or off so you may need a capacitor or something to only turn on when the signal stays at 5V for some time. You will have to continuously power the comparator circuit but can use the comparator output to turn on the rest of the rotator circuit

Hi Elizabeth
Thanks for your help. It could be a great help if you could add a sketch/simple schematic which helps me a lot.
Thanks

I made a sketch to explain but no idea how to copy it into a comment. Maybe someone can help...

This part with some resistors does what I described. The data sheet explains how to calculate the resistors you need. It also shows the circuit inside so you can make it with comparators if you want.
http://www.linear.com/product/LTC2912You will also need a transistor or two to get the 5V to the motor controller.