Serial Receiver is a digital loss-less protocol that uses only 3 wires (signal, power, ground) for multiple channels. As the name suggests this type of receiver requires serial port on the flight controller. This includes SBUS, XBUS, MSP, IBUS, and SUMD.
SBUS (S.BUS, Serial BUS) – By Frsky, Futaba
SBUS is a type of serial communication protocols, used by Futaba and FrSky. It supports up to 18 channels using only one signal cable.
Graupner Hott SUMD
The Graupner SUMD is a serial protocol like Speksat and SBUS. The channels are encoded into one digital signal and have no noticeable latency. Advantages of SUMD are:
- Compared to SBUS, SUMD doesn’t require signal inverter
- Compared to PPM, SUMD has better resolution and no jitter while PPM has only 250 steps and always 4ms jitter
SUMH is a legacy Graupner protocol. Graupner have issued a firmware updates for many recivers that lets them use SUMD instead.
XBUS – By JR
XBUS is used by JR, which supports up to 14 channels in one signal wire. One of the advantages is the tiny time delay between each channel.
more and details information can be found on: https://oscarliang.com/pwm-ppm-sbus-dsm2-dsmx-sumd-difference/