Messages in this thread | | | Date | Mon, 24 Jan 2000 08:50:10 -0500 (EST) | From | "Richard B. Johnson" <> | Subject | Re: Serial Port voltage drops with Linux |
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On Sun, 23 Jan 2000, Alistair Riddell wrote:
> On Mon, 17 Jan 2000, Richard B. Johnson wrote: > > > Hmmm. If his hardware is trying to get power from the modem control > > lines the hardware is broken by design and should be fixed. There > > is no RS-232C specification for this mode of operation. > > And serial mice draw their power from where? ;-) >
From little bits of pizza left laying around.
Seriously, the use of any RS-232C bits for power is completely and totally broken. In the old XT days a serial board containing two UARTs, plugged into an 8-bit slot had lots of power available because DSR was just connected to the 12-volt line. Further, the line-transceivers ran from +/- 12 volts and were capable of driving a model railroad.
Then we got chips on the motherboard and low-power chips in laptops. They all comply with the RS-232C standards but they don't drive mice. Some almost do, depends upon how hungry the mouse is. This is why mouse-ports (bus mice) were provided. One of the wires in that cable is power.
So if somebody is designing a new device, as was the case that started this thread, and they are using "power" from RS-232C, the design is broken.
Cheers, Dick Johnson
Penguin : Linux version 2.3.39 on an i686 machine (800.63 BogoMips).
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