This paper describes the design of a local medium capacity (300 kbaud) computer network based on the ring topology.
With the growing number of microcomputer systems acquired by the University, the need was felt for the ability to enable some of these systems to communicate, not only with common resources, but also for the investigation of distributed processing.
It was decided for speed of implementation to use currently available devices, the most critical of which being the selection of the network interface components. The final compromise based on attainable speed and software complexity was to use the Motorola Advanced Data Link Controller chip.
The next task was the development of the low level ring software. To permit this, a simple ring hardware interface was built around the ADLC chip suitable for SSO bus Motorola 6800 microcomputer systems manufactured by Southwest Technical Products Corp., several such systems being available to test the ring control software.
After developing an interrupt-based control system, it became apparent that the best process would be to recognize specific addresses within frames. Our final design described in this paper therefore uses a dedicated processor per node enabling the decoupling of the network from the host. A M6800 based system was developed with the ability to recover from various network errors such as brief breaks in the loop, corrupt frames etc. With this system, the host need only interact with the network during transmission or reception of frames addressed specifically to it.
As a final step, a SlOO card was designed and is being built incorporating a small M6800 system running the above software. It will enable a number of SlOO 280 based micro-computers used for teaching purposes by the University to be interconnected thus satisfying our original design requirements.