View source for 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.
[[Image:3096B OCTOBUS MPM Channel Controller.jpg |300px | thumb | OCTOBUS card in a [[ND-5700]] crate.]]

=== 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.

{| class="wikitable"
|-
! 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 [[Wikipedia:Transistor-transistor_logic|TTL]]. Non-backwired OCTObus is called ''global'' OCTObus and uses [[Wikipedia:i/Differential_signaling|differential]] cable.

== Sources ==
* ND-14.001.1A DOMINO Standard Hardware Description
* {{Webref |url=http://www.sintran.com:81/sintran/library/libsales/ND-SID001-A1-EN.pdf|title=Sales information ND-5000 series |publisher=www.sintran.com|size=1.1 | original-source=Norsk Data |accessdate=03 August 2010 }}

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