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, with call (select in category) 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 Special Function Description: "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 light