TTL
TTL (Transistor-Transistor Logic) refers back to the TTL integrated semiconductor chips from the early 1960s. They operated on zero or five volts. (low logic being 0V – 0.8V and high being between 2V to 5V).
Today, low power TTL is also available to run on 3.3V in place of 5V. The 3.3V is still within voltage the range of TTL.
Some mounts have a TTL interface that can be used to submit commands to the mount. For example, the SynScan Hand Controller on the Sky-Watcher Mount is a TTL serial interface.
Some mounts also use the low power TTL 3.3V circuitry. The Sky-Watcher AZ-EQ6 Pro is an example of a Telescope Mount that has a low power capable TTL port for connecting to the SynScan controller.
You can substitute the SynScan hand controller (which is also a computer) for your own computer and software and with the appropriate cable, connected to this TTL port and use an application on a computer to replace SynScan computer. A Sky-Watcher Synscan application is available as well as EQASCOM (EQMOD) and GSS (Green Swamp Server).