Shift-F20 can be programmed. This sequence is ignored in VT100 or VT52 Mode as UDKs are not available in these modes. There are a total of 768 bytes available to program the function keys.
Space is supplied on a first come, first serve basis.
Once the 768 bytes are used up no more keys may be redefined until space is freed up. Together they form a single key definition string. They are ignored when an LK401 keyboard is used. The Clear Parameter, Pc, determines which UDKs are cleared, and when. There are only 256 bytes available for the UDK contents.