Hytec Electronics Ltd.

VAX on VME - VME 300 Single Board Computer

HYTEC Electronics Ltd introduced the VME 300 single board computer from AEON Systems, which incorporates Digital Equipments Corporation’s rtVAX 300 subassembly.

”The VME 300 brings the Digital VAX architecture to the industry standard VME bus,” says Richard Tatham, Managing director of Hytec. ”It provides an ideal platform for real time applications.”

The VME 300 includes all the features necessary to support real time data acquisition and control applications in a VME environment. The rtVAX 300 is mounted on a VME 6U x 180mm board, and includes a CMOS VAX processor with 20 MHz clock, Ethernet controller and Floating Point Unit. The Ethernet controller designed by Digital for the VAX environment, includes the ability to reset the processor on request from a host VAX.

Onboard memory configuration of 2,4, 8 or 16 Mbytes are available. This memory is used for instructions (e.g., the ELN kernal) and local storage (e.g., stacks). If further memory is required to handle large amounts of data, external VME memory can be used. The onboard memory is fully dual ported to the VME bus. VAX interlocking intructions are supported both from the local processor as well as from processors on the VME bus. This means that the interprocessor communication support included in the VAX architecture (e.g., interlocked queue instructions) can be used by applications executing on the VME 300.

EPROM Details

Also onboard is room for up to 2 Mbytes of EPROM. When applications are loaded over Ethernet (from a host VAX) a small amount of EPROM is included for extended diagnostics and boot time initialisation. In situations where the VME 300 must exist as a stand alone system, the application can reside in EPROM.

ADDRESSING Details

The VAX can access the VME bus using all VME addressing modes (A32,A24,A16) and all transfer lengths (D32,D16,D8). In addition, the difficulties inherent in supporting a ”little endien” machine (the VAX) on a ”big endien” bus have been addressed. The VME is mapped to the VAX physical memory in 16 Mbyte segments. Associated with each segment is a segment control register (SCR) which directs the onboard data shuffle hardware. This hardware determines if the transaction should use a VME or VAX endien mode. Without support for both kinds of access it would be very difficult to address both memory as well as device controllers. Sixteen segments are available for a total of up to 256 Mbytes of VME address space. Access time to the VMEbus is similar to that of local memory. Aeon has tailored the ELN kernal to configure the segment control registers to connect VME device control register with the appropriate device driver during system initialisation.

SOFTWARE Details

One of the most important features of the ELN kernal is the ability for jobs to exchange messages. Messages can be exchanged within memory (jobs resident on the same VME300), across the VME (if multiple VME300 processors are on the bus) or over Ethernet (to any other VAX processor). When communicating on the VMEbus, message transfer is in excess of 30 Mbytes/second.


Our policy is one of continuous product development and the right is reserved to supply equipment which may vary slightly from that described.



Hytec Electronics Ltd
Post : 5 Cradock Road, Reading, Berkshire, RG2 0JT, England.
Phone : +44 (0)118 9757770
Fax : +44 (0)118 9757566

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Last modified: September 24, 2008