cctalk Digest, Vol 70, Issue 3
mcguire at neurotica.com
Tue Jun 2 10:39:26 CDT 2009
On Tue, June 2, 2009 4:45 am, Johnny Billquist wrote:
>> USB only guarantees to supply 100 milliamps. Up to 500 mA can be
>> negotiated with the controller, depending. Might your older device
>> depend on more amps than the USB adapter can supply?
> Huh? The RS-232-port isn't supposed to deliver any power at all. Some
> devices admittedly abused the RS-232 by using something like DTR to
> actually supply the power needed to drive the thing, but that is abuse.
> But I'd be surprised if a circa-70s modem was ever designed to use the
> power from the RS-232 port to drive the modem itself. I'd expect it to
> have an external power supply.
He's not talking about powering the device, he's talking about driving
the signal lines. Their input impedance isn't infinite, you know!
Port Charlotte, FL
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