FrSky ISRM ACCESS and F.Port

The MavToPass translator was originally designed to connect to the S.Port of a FrSky receiver or transmitter. However, in 2019 FrSky introduced the F.Port, which combined RC control and telemetry into one wire, effectively eliminating the need for SBUS, PPM or PWM pins or pads. F.Port v1 has since been overtaken by F.Port v2, which supports a master/slave architecture, OTA firmware updating and other features. For FrSky receivers, be sure to flash the latest firmware. Bind the receiver/transmitter, select the receiver, go to options, and select F.Port 1 or F.Port2. In Mav2PT select F.Port or S.Port in the web interface. The F.Port version is selected automatically.

From v2.64.0 Mav2PT supports v2.3 7 of F.Port.

See images below

• In general, a new generation of receivers and transmitters is required to support the faster speed of F.Port.
• See here for newer product information: https://www.frsky-rc.com/products/
• Some new receivers, like the Archer M+, offer S.Port, SBUS and F.Port support to help with the transition to F.Port.
• Hardware update boards are available for some older transmitters, but they are relatively expensive
• Only ACCESS firmware supports F.Port. ACCST firmware will not work
• Transmitter, receiver and transmitter rf boards must all be flashed to exactly the same firmware version
• Both S.Port and F.Port telemetry travels on a single wire. The telemetry is termed half-duplex; it travels in both directions, but one direction at a time
• S.Port telemetry pulses are "inverted", with reference to "normal" pulse. To be specific, S.Port pulses are idle low, and various means have been found to invert them for general use.
• Thankfully, F.Port telemetry pulses have conventional, or normal pulse polarity. They are idle high, and do not usually require inversion.
• S.Port telemetry speed is 57600 bit/s, whereas F.Port is 115200 bits/s

Mav2Pass Implications:

• Before v2.63.0, MavToPass translated Mavlink into FrSky DIY (passthu) telemetry suitable for the S.Port only.
• From that version, either F.Port or S.Port must be selected in config.h, and/or in the web interface
• If you get a new FrSky equipment it's likely to be F.Port ready. S.Port might not be available are would require re-flashing of retro firmware.
• If you choose F.Port, remember you no longer need an inverter
• With a few tweaks Mav2PT can decode the RC control telemetry and output it as SBUS, PPM or PWM

Final Note:

While testing using a Teensy 3.2, my Archer M+ and Teensy did not work reliably in one-wire mode at 115200 b/s. I resorted to normal 2 wire (rx/tx cross over), with a two-wire to one-wire converter. Either invert both ends, or don't invert both ends :)

Select your receiver

Now select Options

Now select F.Port1 or F.Port2