The Horus X12S is FrSky's flagship transmitter

The Horus X12S is FrSky's flagship transmitter, with an impressive 4.3 inch, TFT color display. The 480 x 272 transflective display produces sharp, colorful images even when viewed in direct sunlight. The rotary encoder and 6 well placed, tactile pushbuttons allow quick navigation of the various menus and programming their contents. The radio has a solid feel which inspires a sensation of quality. The gimbals are FrSky's best, in CNC milled aluminium with 6 ball bearings and contactless hall effect sensors. Steel cross bars pivoting on ball bearings and a teflon contact surface give the gimbals a very positive feel around center and a silky smooth travel. The Switches and pots are also high quality units. The switches have a positive action, while the pots and sliders are silky smooth.

The most important aspect for any transmitter is maintaining a rock solid connection with the receiver. FrSky is well known for its frequency hopping ACCST technology taking advantage of the entire 2.4GHz band, resulting in excellent range and reliability. The Horus is compatible with most of FrSky's Telemetry and non-Telemetry receivers as well as sensors. With a suitable tx module, the JR style external RF module bay allows operation with Futaba, Spektrum, JR, Aisin, and other receivers. 

The radio has the ability to run two different operating systems. The Horus is supplied with FrSky's FrTX Operating System, which is and easy to program, intuitive menu driven operating system. Advanced users are able to install OpenTX. The Open TX developers have created a visually impressive interface for the feature rich OpenTX 2.2 operating system. Both operating systems are continually being developed and will provide additional features and capabilities to the Horus as time goes on.

ACCST technology
The Horus transmitter makes use of FrSky's bidirectional "ACCST" (Advanced Continuous Channel Shifting Technology) communication system. This frequency hopping technology takes advantage of the entire 2.4GHz band resulting in excellent range and reliability. The most important aspect for any transmitter is maintaining a rock solid connection with the receiver.  ACCST is perhaps the most reliable protocol on the market today.

Being bidirectional means that as well as the transmitter controlling the receiver, data from the receiver can be sent to your transmitter. FrSky knows many things can affect the connection between Transmitter and receiver so RSSI (receiver signal strength indication) is incorporated into all telemetry receivers. The Horus transmitter is continually monitoring the reception quality at the aircraft, and will alert the pilot before signal quality becomes critical. This saves planes and makes the hobby much safer!
Horus has a newly designed internal RF module IXJT with lower latency and higher stability. 
 
 
Receiver Signal Strength Indicator (RSSI) Alerts
Telemetry data is used for real-time monitoring of the received signal quality. Alerts can be set up to warn you when the RSSI value drops below a minimum value, indicating that you’re in danger of flying out of range. Factors affecting the signal quality include external interference, excessive distance, badly oriented or damaged antennas etc.
 
 
Antenna Monitoring (SWR)
The SWR function monitors the efficiency of the radio's transmitter antenna. If the value is above the selected value, an alert can be generated by the system. 
 
 
Antennas
The internal and external antennas are selectable for the internal RF module.
 
 
Support for other RF Systems
The Horus has a normal JR style module bay on the back that will accept modules for other transmitting protocols, including Futaba, Spektrum, and JR. The external bay also allows you to add another FrSky module to your Horus, giving you a total of 32 channels if you use the eight discrete channels and eight serial SBUS channels available on each module.  SBUS is a type of serial communication protocol that allows you to utilize servos specifically designed for SBUS operation and supports multiple channels using only one daisy-chained signal cable.
 
 
Receiver Lock 
The PXX protocol used in the X series receivers allows you to lock a specific model in the transmitter to one and only one receiver. No more flying (crashing) with the wrong program selected. 

Article source: https://article-realm.com/article/Computers/Games/5657-The-Horus-X12S-is-FrSkys-flagship-transmitter.html