Transmitting commands over a serial link

DETAILED DESCRIPTION The present invention provides for the generation of link level commands and responses by varying a minimum number of bits of an idle character to be sent over a single conductor of a two conductor link.
The idle character and the modified character are transmitted in a sequence to form the mentioned link level command or response.
The exact modification of the second character of the sequence determines the command or the response message of the sequence.
Since the second character in the sequence is a modification of the idle character, the sequence maintains the synchronization of the link.
The sequence may be used in place of, or in combination with, frames sent over links of computer I/O systems.
It is thus an object of the present invention to provide a command or response generation apparatus for use an a computer I/O system in which the commands and responses form a part of the link synchronization function.
It is another object of the present invention to provide an apparatus for generating a command or response for use in a computer I/O system in which the command or response is made up of a sequence of idle characters in which the second idle character is a modification of the first idle character.
It is another object of the present invention to provide an apparatus for modifying every other idle character in a string of idle characters, in which only a minimum number of bits are changed to form the modified idle character.
It is another object of the present invention to present a method for identifying the code points of the second modified idle character of an idle character sequence in which each code point may represent a separate command or response.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiment of the invention as illustrated in the drawings.