Re: USB questions


"SMS" <scharf.steven@xxxxxxxxxxx> wrote in message
news:45f97761$0$27180$742ec2ed@xxxxxxxxxxxxxxxxx
M.I.5¾ wrote:
"Barry Watzman" <WatzmanNOSPAM@xxxxxxxxxx> wrote in message
news:45f80e6a$0$28096$4c368faf@xxxxxxxxxxxxxxxxx
Most USB PC Cards supply ***NO*** power unless an external supply is
connected.

In which case they are not compliant with the USB spec. The USB spec
requires a *minimum* of 100 mA to be available from any US port.

Just to run a USB memory key, mouse, keyboard, or joystick requires a few
mA. It wouldn't make any sense to not provide at least the minimum amount
of power. However, these cards could claim that they _are_ compliant, as
long as power is supplied to the card from either another USB port, or
from an AC adapter.


If the port is otherwise active when no external power is connected, but
supplies no power, then it fails compliance with a bus powered device. Such
a device must supply a minimum of 100 mA.


.

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