Help Command (H). Returns entire API in readable format:
KD-PS42> help
-------------------------------------------------------------------------
-- Key Digital Systems HELP --
-------------------------------------------------------------------------
-- KD-PS42 System Address = 00 F/W Version : 1.21 --
-- --
-- Azz : All Commands may have Prefix System Address zz=[01-99] --
-- H : Help --
-- PF : Power Off --
-- PN : Power ON --
-- STA : Show Global System Status --
-- --
-- Video Output Setup Commands: xx = [01-02,A=All], yy = [01-04,U,D] --
-- ( yy : 01=HDBT, 02=HDMI1, 03=HDMI2, 04=HDMI3 ) --
-- SPO SI yy : Set Output to Video Input yy --
-- SPO xx SI yy : Set Output to Video Input yy --
-- SPO xx ON/OFF : Set Output xx ON/OFF --
-- SPO xx VM E/D : Set Output xx Video Mute Enable/Disable --
-- SPO xx DBG ON/OFF : Set Output xx Debug Mode ON/OFF --
-- --
-- Display Control Commands: xx = [01-02,A=All] --
-- SPO xx TV ON/OFF : Set Display xx ON/OFF (Turn TV On/OFF) --
-- SPO xx AV U/D : Set Display xx Volume Up/Down --
-- SPO xx AM E/D/T : Set Display xx Audio Mute Enabled/Disabled/Toggle--
-- --
-- Audio Output Setup Commands: [E=Enable, D=Disable] --
-- SPO AA E/D : Set External Analog Audio Output Enable/Disable --
-- SPO DA E/D : Set External PCM/Digital Audio Output Enable/Disable --