| 摘要 |
There is disclosed herein an apparatus and method for communication between units in a data processing or communication system utilizing light conducting fiber instead of parallel electrical conductor cable. The serial optical link permits potentially higher speed transfers and longer link lengths and utilizes potentially simpler, cheaper and safer construction than is possible with a parallel electrically conductive cable link. Because of the inherent electrical characteristics of copper cables, parallel links are limited to transfer rates of approximately 5000 bytes per second and 100 feet maximum length. By taking advantage of the greater bandwidth of optical fibers and utilization of manchester or Bi-phase L coded serial data transfers and time division multiplexing, higher transfer speeds and longer link lengths may be achieved. Higher data transfer rates may also be achieved utilizing electrically conductive cables, however cables of larger and more expensive construction would be necessary to eliminate some of the inherent speed limiting properties in cheaper cables. With optical cables, the large bandwidth allows the use of relatively cheap components and a reduction in the number of lines needed between the CPU and the peripheral. Further, the larger bandwidths allow a potentially higher data transfer rate with some protocols despite the fact that serial format is used. In the preferred embodiment, a trigger generator senses when transfer of a data packet is desired. At that time, a header generator generates a header for the data packet, and a Manchester encoder latches the parallel data into a shift register with the first 3 bits used to generate the header. The header bits are shifted out of the shift register. A header generator modifies the clock signal to a Manchester encoder producing a non-Manchester data header. After the header is out, the data is encoded in Manchester format. A receiver at the opposite end of the optical link recovers the clock from the manchester encoded data, detects the header, and shifts the data into a shift register where it is transferred out in parallel format. |
