The .pdf files attached contain the public documentation for the GHST serial protocol.
The Rx protocol is that used between the Ghost receivers, and flight controllers. This protocol is implemented in open source flight controller code such as Betaflight, iNav, Ardupilot, and PX4.
The Tx protocol is that used between the Ghost transmitter, and the R/C remote. This protocol is implemented in open source R/C software such as OpenTx, and EdgeTx. 


Note that a unique aspect of the Ghost protocol design is that the protocol on the Tx side does not necessarily need to match that used on the Rx side. As an example, GHST may be used between EdgeTx and the Ghost transmitter, and SBus may be used between the Ghost receiver, and the flight controller. 

Optimal performance however will be reached using GHST both sides of the link.