Design of Manchester II bi-phase encoder for MIL-STD-1553 protocol

Data bus standards are inevitable in all electronic systems. In avionics systems the medium used for data transfer should be highly reliable and communication should be done with a minimum amount of hardware. MIL-STD-1553 is one such data bus standard which is mainly used in military avionics applications for data transfer between critical systems in an aircraft. It is a bidirectional, digital time division multiplexed data bus which eliminates the use of point-to-point wiring. 1553 uses Manchester II bi-phase encoding scheme. Compared to other encoding schemes Manchester coding has some advantages like easy error detection, high noise immunity etc. Even with more bandwidth requirement 1553 protocol uses this encoding because of its low error rate. In this paper we discuss the design of a Manchester II bi-phase encoder and decoder for the 1553 data bus system. With the presented method, the encoder and decoder is modeled as state machine in HDL. This is explicitly designed for encoding and decoding the words of 1553 data bus protocol.