Multiple DMMs control via serial

[vitvip]

Sorry, I know this issue has been already addressed many times, I will sure read on. However, I was not able to find the answer immediately, so any help is greatly appreciated.

We need to acquire data simultaneously from 3 Keithey 2000 DMMs. They are connected to COM1 to 3. 2 ports are on the motherboard, 1 extra is on generic add-on card. Naturally, 2 ports share IRQ.

The problem is that DMMs connected to the ports that share IRQ cannot be used at the same time. Is it normal and what are possible resolutions? Do any cards exist that allow interrupts for COM ports other than IRQ3 and 4? Possibly USB-to-serial converters?

Thank you in advance!

Regards,

Vitaly

[Jonnie_5]

I've used Hawkings USB-serial converter w/ great success to get around port issues.

http://www.hawkingtech.com/products/productlist.php?CatID=40&FamID=106&ProdID=22

Message Edited by Jonnie 5 on 04-20-2006 06:29 PM

[tuba]

National Instruments sells a full range of Serial Interfaces, including PCI cards, USB devices, and several other options.  These are plug and play and you won't have to worry about any resource assignments.

-tuba

[vitvip]

Thanks, but I am still a little confused. These expensive cards have up to 16 ports on them, so several ports for sure share one interrupt and they are still supposed to work.

Thanks.

[tuba]

It is perfectly normal for PCI devices to share interrupts.  In the case of the NI serial cards, the standard Windows serial driver is replaced with NI-Serial, which takes care of getting your data to the correct port on the card.  You will definately be sharing resources, but that is just fine.

I assume that you are using Windows 2000 or XP.  If so, take a look at your device manager.  On the View menu, choose to view resources by type, and then expand your IRQ section.  You will probably have a bunch of shared IRQs already on your system!  My computer has 8 devices on IRQ 5!

-tuba

[vitvip]

True, I just encountered numerous reports about problems with COM ports sharing IRQ.

I cheched, on my system 2 conflicting ports are on PCI bus. They share IRQ3, while IRQ4 is assigned to COM3 on ISA add-on card. If I remove the card, the ports are automatically set to different IRQs and can be used without problems. But I do need 3 DMMs.

I found out that on some motherboards IRQ for COM ports can be changed freely, while on others (including mine) one can only choose from several configurations of I/O address-IRQ with only standard IRQ3 and IRQ4 options. Not sure if in matters.

Still, I get "Error -1073807360 occured at VISA Open in ke2000 Initialize.vi"

[tuba]

"Standard" COM Ports (Like those on your motherboard, or your ISA card) generally only work on a predefined set of IRQs, and are unable to share IRQs because they are "Legacy" devices that have been carried down since the early days of the PC.  Newer interface cards like the NI boards and others replace the standard Windows driver with a more modern driver which doesn't rely on each port having its own IRQs.  This is generally true for USB to serial adapters as well.

-tuba

[Al M]

Vitvip do you have any more questions regarding your resource conflict errors or have you been able to find a sufficient answer?  If you have any specific questions regarding our products please feel free to ask.  Cheers.

Al M.

Applications Engineer

National Instruments

 

[vitvip]

Thanks a lot everybody! Well, I find tuba's explanation perfect and thus I rated it 5. I think a while ago one could mark the thread "My answer has been answered" but I don't see this option now. Am I missing something? Or was that another forum? 🙂 Sorry, I am generally trying to be polite and grateful but don't want to waste other's time and bandwidth.

Thanks again!