Abstract: A digital communication system employs a technique of effectively controlling the size of the bytes making up a field of data to be serially transmitted from one station to another, particularly one wherein the byte size may be selectively changed during the transmission of the data field. Assembly of a transmitted data field is controlled so that it includes an encoded data byte, termed a first pre-header byte, which contains information as to whether or not a change in the byte size of the data field is to occur. If the first pre-header byte indicates the occurrence of a byte size change, it also will contain a code representative of the size of the change. In addition, for a change in byte size, a second encoded data byte, termed a second pre-header or count byte is generated and immediately follows the first pre-header byte. The count byte contains information which specifies the length of that portion of the data field which precedes the occurrence of the change in byte size.

Abstract: Communications between processor terminals are carried out through the use of communication adapters. Each adapter receives selected control signals for transmitting or receiving data over a serial communication link to or from a remote terminal. The transmission portion of an adapter includes pretransmission control circuitry which receives control signals and stores transmission control signals which are used to control the format and serial transmission of a frame of data to a remote terminal. Each frame of data is begun and terminated with a uniquely encoded flag byte. Following the first flag byte are successive address and control fields. An optional information field may follow the control field and may include encoded information designating a dynamic change in the byte size of the data.

Abstract: A technique and implementation of generating and supplying synchronization and error checking signals to a serially transmitted data stream includes the generation of flag bytes which define the end boundaries of the serial data stream, an abort character for aborting the transmission of a frame of data in response to certain conditions, and a diagnostic evaluation character inserted into the data stream. In addition, the invention provides a technique for ensuring that the unique binary code by which a flag byte is defined occurs in the transmitted data stream only where intended. The flag code has been chosen to contain a prescribed number of consecutive one bits, (i.e. -- six) flanked by zeroes, and circuitry monitors the contents of a data frame as it is being serialized out for transmission to a remote terminal at times other than during flag transmission.