Enhances AS 2751 (ISO 7809) by reflecting the broadening of the definition to the Un-numbered Information (UI) command/response function to allow its use in both operational and non-operational modes of operation. It clarifies the fact that a command frame may be transmitted simultaneously to more than one, or all, of the stations in a multipoint configuration through the use of a few corrections to improve understanding and remove ambiguities. This Supplement is identical with and has been reproduced from ISO 7809: Addendum 1-1987.