Bus Error when accessing A24 space on a VME device with VXI-VISA and VME-MXI-2

[bnemmers]

I am trying to access A24:D8 register space on a VME card, but I get a bus error using viIn8 and viOut8 with VXI-VISA on a VXI controller running Win2k across a VXI-MXI-2 <-> VME-MXI-2 link.

I found the following entry on your site, but I do not if or how it applies to my situation:

I Cannot Access A24 Space on a VME Bus with a VME-MXI and an AT-MXI-1 on a Windows NT System.

Product Group: VXI Software

Product Name: NI-VXI for AT-MXI for Windows NT

Version/Revision: 1.0

Problem: With a VME device, bus errors were received when trying to do a VXIin or VXIout to the address in A24 space. The device was successfully edited within the non-VXI device editor portion of VXIedit. Resma
n acknowledges that the device has a base address of x0000 and has requested 4 MBytes of space in A24 space, but the bus errors were still received.

Solution: Use VXIedit to insert x4700 into registers A, C, E and 10 of the the VME-MXI. This allows the entire range of VME address spaces (A16, A24 and A32) to be mapped to the MXI bus. You can then access A24 Space.

Related Links:


Fixed Version:

Report Date: 08/01/96

Last Updated: 07/19/2002

Document ID: 0O076NGJ

[David S]

Hi bnemmers,

Thank you for contacting National Instruments. First, let me address the KnowledgeBase that you referenced. That KnowledgeBase applies to the VXI-MXI, not the VXI-MXI-2. A similar solution may help, but I will explain that solution last.

You said that you could not access A24 space on you instrument. Do you have problems accessing A24 space on this particular instrument or on all of your instruments? If you can not access A24 space at all, then there could be a problem with your MXI-2 controller or with its configuration.

If it is a single instrument that is causing problems, then I suspect there is a problem either with that particular instrument or with the configuration of that particular instrument. If possible, I suggest you test another working instrument in this system. I also suggest you test this instrument in another system that you know is working.

You mentioned that you are using a VME instrument. If this is the case, then I want to make sure that you have the VME instrument properly configured in Measurement and Automation Explorer. When you add a VME instrument using the "Create new VME Device" option in Measurement and Automation Explorer, you must make sure to add A24 space as a resource in order to communicate in A24 space. When you add this resource, make sure that you select an appropriate range.

As I mentioned above, it is possible that the MXI-2 interface is not configured properly. It is possible that A24 access is not configured properly and that your device is never even seeing a request to read or write a register. There is a register on the MXI-2 that controls A24 access. This register is called VWR2, Extender A24 Window, and is located at 0xE of the MXI-2's A24/A32 address space. You can read this register using viIn16. If you are using A24 space, then bit 14 should be set to 1 to enable A24 address mapping. Bits 10-8 control the size of the A24 window that is mapped, and bits 7-0 control the base of the A24 window. To make sure that A24 space is enabled and mapped, try writing 0x7800 to this register using viOut16. Assuming that you have opened a VISA session to your VXI-MXI-2 or VME-MXI-2, you would use viOut16(visa session, A24, 0xE, 0x7800). Some of this is explained in the VME-MXI-2 User Manual available at http://digital.ni.com/manuals.nsf/webAdvsearch/68409BFF568BB6118625665F005A0A41?OpenDocument&vid=niwc&node=132100_US.

I hope this helps. If you are still encountering problems, I suggest you call and talk to an Applications Engineer. Please generate a phone support request at http://www.ni.com/ask. When you do that, you will be given a Service Request Number and a phone number to call. When you call that phone number, you will be routed directly to an Applications Engineer.

Regards,

David Shatila
Applications Engineer
National Instruments