User manual

Appendix B Programmable Configurations

VMEbus Requester

Request Level

The VXI-MXI-2 uses one of the four VMEbus request levels

(0 to 3) to request use of the VME Data Transfer Bus (DTB). The

VXI-MXI-2 requests use of the DTB whenever an external MXIbus

device attempts a transfer that maps into the VXIbus mainframe.

The VXI-MXI-2 uses VMEbus request level 3 in its factory-default

setting, as required by the VXIbus specification. This is suitable for

most VXIbus systems. However, you can change the VXI-MXI-2 to

use any of the other three request levels (0, 1, or 2) by writing to the

EEPROM. You may want to change request levels to change the

priority of the VXI-MXI-2 request signal.

Fair Request

The VXI-MXI-2 is always a Release On Request requester. However,

you can configure whether the VXI-MXI-2 acts as either a fair or unfair

requester on the VMEbus. By default, the VXI-MXI-2 is a fair

requester. For more information on the different types of requesters,

refer to the VMEbus specification.

To change the VMEbus requester type of the VXI-MXI-2, write the

EEPROM byte at offset 20B5 hex from the VXI-MXI-2 base address.

The following table gives the value that should be written for the

corresponding requester type. The values shown in the table are

hexadecimal.

Bus Request Level Fair Requester Unfair Requester

Bus Request Level 3 07 (default) 17

Bus Request Level 2 06 16

Bus Request Level 1 05 15

Bus Request Level 0 04 14