Data General AViiON 5000 Series, Customer Documentation

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Appendix E
Assigning VME Data Bus and
Interrupt Priorities
This appendix discusses VMEbus priority issues and provides guidelines for
assigning VME data bus and interrupt priorities within the Data General AViiON
systems environment. Primarily, the discussion centers around the VME Data
Transfer Bus (DTB) and interrupt priority architecture and the demands that
various types of VME controllers place on bus and system resources. This
information is very technical—it is intended for properly trained persons only.
Reference Documents
This appendix provides practical guidelines for deriving VMEbus DTB and interrupt
priority settings. For further details on these topics as well as other aspects of the
VMEbus, refer to the following documents:
The VMEbus Specification, Rev. C.1 (Motorola Inc., P/H HB212)
IEEE Standard for a Versatile Backplane Bus: VMEbus
(ANSI/IEEE Document, P/N ANSI/IEEE Std 1014–1987)
The VMEbus Specification manual from Motorola Corporation is particularly useful. It
defines how all hardware connected to the VMEbus will move data from one point to
another. It provides a detailed description of the physical interface to the VMEbus, and
defines methods each connection can use to gain access to bus resources.
Data Transfer Bus (DTB) Priority Arbitration
Methods
The following sections describe the DTB priority methods used on Data General
AViiON systems. Some of the important terms that you should understand are:
Bus arbitration A term for the process by which a VMEbus slave or master
device requests and obtains bus resources.
Master A term for a controlling device on the VMEbus. Can both
initiate data transfers and respond to requests from other
master devices.
Slave A term for a subservient device on the VMEbus. A slave
device responds to requests from master devices.
Arbiter The host logic that manages VMEbus arbitration.