Token ring access control protocol circuit

摘要

A token ring access control protocol circuit which includes an M/T converter for converting incoming serial data in differential Manchester encoded form into transitional encoded form. Next the data is fed into a shift register and held temporarily while it is compared with preset sequences to determine if it is a starting delimiter or an ending delimiter. If a starting delimiter pulse is generated and used to synchronize subsequent circuitry if required. Data from the shift register is continuously sampled with at least a 2 baud delay by a data sample latch circuit which provides and output line for data values and another output line for code violation signals. The data values and code violation values go to a data receiving circuit which processes the data, and loads it onto a local data bus for transmission to other parts of a token ring control system. A data insertion multiplexer has inputs which are connected to the serial data output of the shift register, the output of the transmit machine and to various state machines for inserting modified data into the serial data path. The output of the data insertion multiplexer goes both to a transmit output multiplexer and to a fairness delay.