Re: Serial Port voltage drops with Linux

From: Thorsten Kranzkowski (th@Marvin.DL8BCU.ampr.org)
Date: Mon Jan 17 2000 - 20:09:58 EST


On Mon, Jan 17, 2000 at 03:07:35PM +0100, Jens Benecke wrote:
> Hi,
>
> The situation is this: When we connect the hardware to the serial port, the
> signal amplitude breaks down to lower than +3V (which is miniumum for the
> PC to detect a "0"). With DOS, the signal amplitude varies from -10..+10 V
> (approx) for 1/0 signals. With Linux, it's -10..<+3V, and that is not
> enough.

Umm - Linux doesn't adjust Power supply voltage levels and it doesn't swap
new serial line driver IC's in place either :-))

You have made __double__ shure you didn't connect two output lines together
(eg. TxD from computer to TxD from your device)? And you also checked your
GND connection?

> Do you have any further ideas about this? Why do the ports behave so much
> differently (no matter if we start setserial or not) when using Linux? In
> theory (yeah, right) it's hardware that should behave the same under any
> OS, at least in respect to voltage levels and power consumption?

Yes, they _do_ behave equally :)

> BTW, we tried three different serial port hardware boards (ISA) so the
> hardware should not be at fault.

...and have booted DOS on the very same computer with the very same ISA-boards
and your device?

How did you build the power supply of your device? An external AC-powersupply
('Netzteil') or from some unused 'to be set to 12V' status lines? If the
latter, are they set to 'high level' when you connect your device?

> I have put the QBasic source and the C source at
> http://www.pinguin.conetix.de/serial.zip, perhaps someone can shed a little
> light on this. There is also a complete DOS floppy boot image including
> QBasic and the .bas file for those who do not have a bootable DOS handy
> (dos.img.gz).
>
> Thanks a lot!

Keine Ursache!
Thorsten

-- 
| Thorsten Kranzkowski         Internet: dl8bcu@gmx.net                        |
| Mobile: ++49 161 7210230        Snail: Niemannsweg 30, 49201 Dissen, Germany |
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