OCTOBUS

Octobus (or OCTObus, as it was written in some documentation) was a high-speed serial command bus for system-internal high speed signal/command transfer. It could send short messages used for synchronization of directly coupled processors in multi-processor configurations including DOMINO I/O controllers.

OCTObus physical implementation

The MPM-5 (MultiPortMemory) system was extended with the physical wiring and features for Octobus support and was then called Multi-Function bus, or MF-Bus, introduced with the ND-5000 series.

OCTObus purpose

Octobus was a part of transforming the original ND-500 design, where the ND-110 processor was an I/O bottleneck, to a multi-processor system with DOMINO I/O boards connected directly to the MF-Bus. The role of OCTObus was to manage and synchronize the processors.

OCTObus protocol overview

• An OCTObus message is 32 bits. It includes priority, destination, source, information, etc.
• Each device connected to the OCTObus is called a node.
• There can be up to 62 nodes on one OCTObus.
• An OCTObus can be bridged to another OCTObus if 62 nodes isn't sufficient.
• One node must be set up as MASTER. This node supplies the OCTObus clock (XCLK)
• Any node can be set up as MASTER, the MASTER node is not special.
• All nodes can take control of the bus, by issuing a request (XREQ) intercepted by the MASTER.
• Power failures are tolerated by all nodes.
• Retries are handled by hardware.

OCTObus signals

• XREQ - Transmit request
• XCLK - Clock
• XDAT - Data
• XRFO - Refresh oscillator

OCTObus data rate

Data rate depends on cable length.

Cable length in meters	Clock frequency in MHz	Data rate in Mbits/s
6	4	1.0
60	1	0.250
120	0.5	0.125

OCTObus cabling

The internal backwired OCTObus in the MF-Bus is called a local OCTObus and is TTL. Non-backwired OCTObus is called global OCTObus and uses differential cable.

Sources

• ND-14.001.1A DOMINO Standard Hardware Description
• "Sales information ND-5000 series" (found at www.sintran.com, original published by Norsk Data). Filesize 1.1 MB. Accessed on 03 August 2010.

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