USB to Serial Port Converters

clintin at linuxmail.org clintin at linuxmail.org
Sun Feb 28 22:04:54 UTC 2010


One simply can google "usb to serial adapter" but make sure it is a 
supported device in Linux.

The adapter does more that just putting 5 volts on the serial connector 
and provide a handshake; it may require a driver to create the serial 
resource.  These solutions were even problematic in Windows as I recall.

On recommendation that I would also make is the use of a USB port 
expander that has its own power supply so that you don't overload or 
damage the computer.  I almost damaged my laptop from a device that 
wanted a lot of current from the USB port.  Karl, you might try your 
adapter with such an external port adapter as it current requirements 
may explain why the device is "dying" shortly after you plug it in.

If you really want to do know the characteristics of serial 
communication, I suggest you check out the RS-232 specification.

Clint


-----Original Message-----
From: Nils Kassube <kassube at gmx.net>
To: ubuntu-users at lists.ubuntu.com
Sent: Sun, Feb 28, 2010 2:07 pm
Subject: Re: USB to Serial Port Converters


Karl F. Larsen wrote:
>   A year or two ago I bought one of these, with CE  FC as the
> maker of this device. It does not work well at all.

Can you tell us the USB ID so we know which part doesn't work? You can
find it with the lsusb command while the device is connected compared 
to
the output with the device disconnected.

>   I need one that reliably puts 5 volts from the USB onto the
> proper serial port pin.

There is no pin designated for 5V on a serial port [1], therefore I
don't think you will find such a thing.

> I also need to use the serial port
> XON/XOF flow control.

XON/XOFF flow control is available with every such part because it 
works
over the RX/TX signal lines. It is more a question if the software on
both ends supports XON/XOFF.

>   Can anyone give me a clue as to what to buy? My old one
> provides the 5 volts for about 15 seconds and quits.

Do you want to misuse a signal pin as a supply pin for the equipment
connected to the serial port? Then the device might detect your load as
a short circuit and shuts down the output. The problem is that the
available current is very limited on the signal lines. Maybe you should
consider an external power supply, e.g. directly from another USB port.


Nils

[1] <http://en.wikipedia.org/wiki/RS-232>

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