FrSky XM+ Receivers are now coming installed with ACCST 2.0 firmware. This is not compatible with ACCST 1.0 controllers and firmware updates will be required if there is a firmware mismatch. Firmware can be found here: https://www.frsky-rc.com/xm-plus-mini-sbus-non-telemetry-full-range/ (Select history firmware download for ACCST 1.0 firmware)
FrSky XM+ Ultra Mini SBUS Receiver, ONLY 1.6g
Specification
Dimension: 21.5x12x3.5mm(LxWxH)
Weight: 1.6g
Number of Channels: Up to 16CH from SBUS(CH1~CH15 for PWM, CH16 RSSI for FC)