Abstract: An 8B:10B serial data transmission code is described, which provides an overall balance between ones and zeros, a code run bound of 4, and a worst case transition density of 40%. In addition, the code provides two special control characters which are unique in the coded bit stream and can be used for synchronization. The data can be encoded using a 256.times.8 ROM, and decoded using a 1024.times.6 ROM, with two bits being transmitted unencoded.

Abstract: A data transmission system is formed from a series of data transmission loops (2). Each loop includes an interface unit (3) for an attached device and is connected at either end to a synchronizing and switching module (5) in a central unit. The loops (2) are connected by the modules (5) into a continuous data-transmission path connecting the interface units in sequence.The interface units 3 each acts as a synchronous repeater and/or a source of fresh data. To prevent the accumulation of jitter in the clock signals derived in the interface units each module (5) contains a first-in first-out buffer (25) in which the data is resynchronized to a common clock source (7) used by all the modules. The modules (5) also bypass any loop which contains an inoperable unit over a link (35).

Abstract: A communicating network in which encoder/decoders are joined in a ring by transmission links. Data passes over the links as a carrier having two cycles per bit period. The amplitude of the carrier in any bit period is non-zero and represents the value of the bit. In each encoder/decoder the carrier is recovered by a tuned circuit, the clock is recovered by dividing the carrier and the data is recovered. The same carrier is remodulated with the output data. The whole system forms an oscillatory system which sustains the carrier at a frequency which varies if the properties of the ring change.The specification also describes the use of a modulated carrier in conjunction with a filter blocking frequencies below 25 MHz to give good noise immunity.