How to Trigger the Terminal

Ground the input using a relay when no operation is desired (0V). When the ground is removed (energizing the relay), any voltage between .66 and 5 should operate the drive in a forward condition.

If you cannot differentiate between .66 and 5, then a more robust design should be implemented...probably available from the manufacturer.

There are commercial alarm modules available from vendors of signal conditioning.

In your case, you need a DC alarm module's input can be ranged 0-1.0Vdc.

You set the alarm to operate as a 'high" alarm with a setpoint of 0.55Vdc so that it trips when the input voltage is greater than 0.55Vdc. You need some difference between the trip point 0.55 and 0.66 because the 0.66 might shift slightly over time.

The output relay will change state and you can switch whatever voltage you want through the relay's dry contacts.

It's a commercial, easily understood concept, especially if you label it "high alarm SP 0.55Vdc".

http://api-usa.com/pdf/api/api1000g-1020g.pdf

You need to incorporate a micro-controller with logic outputs for forward, reverse, enable etc. The input will be serial digital signals 0.66 v or 1 volt high nad 0 volt low. If you have a series of say 8 bits- you can have 256 combinations. If you have just 3 digits - you can get 8 combinations. This is similar to double clicking a mouse button or single press. Now it is 3 presses - to give you 8 combinations. Even 2 digits gives you 4 combinations. You should have a start, an end and 2 digits in between.