INXTCHR returns a single key pressed on the terminal. In the VAX/VMS environment, it will intercept all control keys (including <ESC>) except without echoing to the screen. Opens a direct IO channel to the terminal driver using SYSQIO. This routine is used by the PAUSE and CURMOTION routines.
key = INXTCHR()
key (I): (returned) terminal character (ASCII value)
if key < 0, an error reading terminal input has occured.