National Instruments PCI-8430 - Page 183

HowdoIresolveserialUSBpowerconflicts?
TheUSB-232,USB-232/2,USB-232/4,USB-485,andUSB-485/2are
high-powerbus-powereddevicesthatrequiremorethan100mAduring
normaloperation.Thus,theymustbepluggedintoanexternallypowered
hubthatcandeliverupto500mAperUSBport.IftheUSBnetworkdoes
nothaveenoughpowertosupporttheUSBserialhardware,anda
systemdialogboxinformsyouthatthereisnotenoughpowerforthe
device,reconnectthehardwaretoanexternallypoweredhub.
TheUSB-485/4isaself-powereddevicethatrequiresexternalpower.If
thedeviceispluggedintoaUSBport,andthedevicedoesnothave
power,itwillnotenumerateandtheportswillnotshowintheDevice
Manager.Toensureproperportenumeration,alwaysmakesurethe
USB-485/4hasexternalpowerbeforeconnectingittotheUSBnetwork.