Optical data bus having a statistical access method

DETAILED DESCRIPTION In an optical data bus of the above species, the object of the present invention is to obtain, particularly with CSMA/CD access methods, the most simple as possible control circuits for the communication portion.
The above object is achieved, according to the present invention, in the type of system generally set forth above which is characterized in that the encoder is a Manchester encoder which effects Manchester encoding of the data to be output onto the data bus, in that the decoder is composed of a Manchester decoder which decodes the Manchester encoded data supplied thereto, and in that a clock recovery device is provided which reacquires the clock contained in the Manchester-encoded data from the Manchester-encoded data and the decoded data.
The above solution, accordingly, is based on the known principle of encoding the useful data in accordance with the Manchester techniques in order to reacquire the clock in the receiver in a simple manner.
This type of decoding enables the control circuits in the transmitter portion, in the receiver portion and in the collision recognition portion to be simplified and constructed with fewer modules.
Further, no marks are required for the beginning and the end of the useful data, these marks having to be separated again from the useful data in the receiver.
The data bus of the present invention requires twice as much bandwidth as the aforementioned proposed data bus.
Its structure, however, is more simple and is therefore less susceptible to disruption.
It can be advantageously realized everywhere that an optical transmission system comprising transmitters, fibers and receivers still contains sufficient reserve that the system can be operated 100% redundancy.
A particularly simple and advantageous embodiment of the data bus of the present invention is characterized in that the Manchester decoder comprises three delay lines in which the supplied Manchester-encoded data are respectively delayed by half the clock duration, by a duration lying between half the clock duration and the full clock duration, and by the full clock duration of the clock contained in the supply data