Errors While Using Multiple USB-CAN Devices Through a USB Hub

Updated Jul 9, 2018

Reported In

Driver

  • NI-CAN

Issue Details

Why am I having initialization errors when attempting to use multiple USB-CAN devices through a USB hub? All the devices appear in MAX and work when attached to a dedicated USB port.

Solution

USB-CAN devices from National Instruments draw 250mA of current. A standard USB 2.0 port can supply 500mA, so when connected directly to the port a USB-CAN device can be bus powered. However, a standard down stream USB hub port can only source 100 mA, so you will encounter issues trying to initialize your CAN device. 

In order to use multiple USB-CAN device on a USB hub you must have an externally powered USB hub that can source a minimum of 250 mA to each port.

 

Additional Information

NI recommends against using USB hubs, as the specifications all vary with each manufacturer. There are power and throughput limitations for each bus that are unknown. Even if the device appears to be functioning, the hub could lose data packets, which is out of the device's control. 

 

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