Maximum number of USB devices possible

[cpede]

What is the maximum possible number of NI USB devices possible. I believe that the maximu number of USB devices an one USB bus is 128, but what about the AX utility etc.

-cpede

[Morini]

Hi cpede,

The USB standards specify that there can be a maximum of 127 USB devices connected to a single host controller: "Up to 127 devices, including the hub devices, may be connected to a single host controller" (http://en.wikipedia.org/wiki/USB) 

In practice, you will run out of bandwidth long before that(Depends on the device types -- WLAN uses more bandwidth than usb mouse ASO). You should also consider your current consumption with so many devices(100-500mA depends on selfpowered or external powered).

Can you tell me how many NI USB devices do you need for your application? I'm not familiar with the AX utility you mentioned in your thread, can you post a link to this utility?

Thanks!

[cpede]

The AX utility should have been MAX (NI Measurement & Automation) . MAX list all the devices found, I guess this also has a maximum.

My application is a flexible system, why I need to specify a limit of the number of USB NI devices that can be attached.

-cpede

[Morini]

Hi cpede,

You can compare MAX with Windows DeviceManager to a certain extent. It tabs into USB discover functions in Windows and you can't get more NI USB devices connected to the system than the bus standard using MAX.

I hope it makes sense.

Thanks!

[Tiptop]

cpede,

I work on the DAQmx driver, and can tell you that we have done some internal testing with ~20 devices hooked up to one machine.  As has already been said, the system bandwidth will fall, and it is also important to note that you will need powered hubs.  Self powered USB hubs will lower the amount of devices you can have because of the limited power from the USB Spec. 

Most importantly, I've found that high quality hubs and cables can save you lots of time.  Some of the lower quality hubs on the market can lose usb messages, which causes your NI USB devices to work improperly.  I've also seen USB 1.1 cables used on a USB 2.0 devices, causing Windows not to recognize it.

Here is some more information.

http://ae.natinst.com/operations/ae/public.nsf/web/searchinternal/22e3aa18078ceda886257195005574a4?O...