Means to differentiate between commands and data on a communications link

DETAILED DESCRIPTION It is therefore an object of this invention to differentiate between commands and data while requiring minimum bandwidth, providing dc balance and sufficient bit transitions for the receiver to maintain bit synchronization, and not requiring bit stuffing.
Furthermore, data may arrive at the transmitter in bursts with idle periods in between.
After an idle period, the receiver must be able to determine when the link becomes active again.
Accordingly, this invention provides a method of transmitting a stream of information symbols so that data information symbols can be easily distinguished from command information symbols.
Information symbols in a set D, representing data or commands to be transmitted are first encoded into a larger set E of code symbols.
An encoded information symbol may either be interpreted as a data symbol or a command symbol, depending on the context as explained below.
One code symbol, S, in E, which does not represent an information symbol in D, is used to delimit between commands and data.
When the transmitter wishes to send a command, it first transmits the delimiter S, followed by the encoded command.
When the transmitter wishes to send data, it first transmits the delimiter S, followed by a command representing Start-Of-Text, followed by the encoded data.
At the receiver, whenever S is received, the receiver awaits the arrival of the first symbol that is not S.
This non-S symbol is interpreted as representing a command.
Whenever the Start-of-Text command is received, all succeeding symbols are interpreted as data until S is received again.
This Start-Of-Text is also used to inform the receiver that the transmitter has transitioned from an idle state to a state where data is transmitted.
After leaving its idle state, the transmitter automatically inserts a Start-of-Text after an S symbol before it begins transmitting data.