Analog differential output (RP, RN, LP, LN) When is used with a box: the highest protocol Clear pairing information: the highest protocol LDAC (5125 default). Support serial port AT commands, 115200, N, 8, 1 Support Android APP to modify Bluetooth name (support any language), pairing password, custom EQ, switch prompt tone. 5125 supports , AAC, , APTXLL, APTXHD, LDAC,Function keys: KCOM, PLAY, VOL+, VOL-, P/V-, +, MODE, high level 3V3 is valid. Bluetooth connection status output foot BT_HL (Bluetooth connected: output high 3V3, Bluetooth disconnected: output 0V). Button Description: "VOL+": short to increase volume, long to increase volume, "VOL-": short to decrease volume, long to decrease volume, "+": short to play next song, long to increase volume, "P/V-": short to play previous song, long to decrease volume, "PLAY": short to play/pause/answer/hang up, long to reject "PLAY": long for 3 seconds and release to force pairing mode,long for 6 seconds and release to clear pairing list "PLAY" + "VOL+": long for 1 second at the same time to enter host mode and search "PLAY" + "VOL-": and hold for 1 second to enter slave mode and is searched "VOL+" + "VOL-": and hold for 1 second to disconnect "+" + "P/V-": and hold for 6 seconds and release at the same time to clear pairing information and pairing password, and reset MODE/ key: Bluetooth is not connected to the mobile phone: Short , host mode search (with prompt sound) Double click, slave mode is searched(with prompt sound) and hold for 6 seconds and release,clear pairing information,clear pairing password,and reset(with prompt sound). After Bluetooth is connected to the mobile phone:Short : play pause;Double click:next song. and hold for 3 seconds and release, disconnect the mobile phone and enter pairing mode. LED light: Pairing status, two lights flash alternately;pairing successful, single light flashes DCOM,