Methods and apparatus for implementing a high speed serial link and

Abstract

Methods and apparatus for implementing a high speed serial communications bus with no data loss include a point-to-point bus and a multi-user bus. Both buses are easily implemented in the system software of virtually any microprocessor and make use of virtually any one, two, or three I/O pins of the processor. The point-to-point bus allows two processors (bus users) to communicate via one, two, or three lines coupled to any two I/O pins of each processor. The multi-user bus allows an unlimited number of processors to communicate via three lines coupled to any three I/O pins of each processor. The methods of the invention include providing each processor with communications software by which data is transmitted and received one bit at a time by asserting one or more of the lines of the bus according to a fixed protocol. In the point-to-point bus, when transmitting a ZERO, the first line is a data line and the second line is an acknowledge line. When transmitting a ONE, the second line is a data line and the first line is an acknowledge line. An asserted data line is held asserted until transmission is acknowledged. In the multi-user bus, three physical lines are used, having functions D0, D1, and ACK. The functions of the physical lines are rotated according to the last bit transmitted and received. The functions don't change until all bus users acknowledge receipt of the transmitted bit.