Re: [NTLK] USB to serial converter question

From: W. Sierke (ws_at_senet.com.au)
Date: Wed Nov 19 2003 - 21:15:06 PST


"Dan" wrote:
>
> Actually as I said, it does have a serial port. But I have several serial
> devices and I have to power down, unplug old device, plug in new, power
up.
> Kind of anoying. Serial is fine except for that. As for outdated, well
all

Dan, it's highly unlikely that you need to power down to swap serial
devices. If you're doing this out of fear of causing damage to your PC or
equipment, all I can say is in 20-odd years of working with RS-232 serial
devices I'm not aware of one instance where plugging or unplugging has
caused any damage. RS-232 is typically an electrically robust interface and
has no problems coping with connection or disconnection of "live" devices
(unlike various other types of interface). Nevertheless, PC/Notebook makers
are known to deviate from the standards so keep the following precautions in
mind when changing serial connections:

 - avoid shorting the pins on the male connector. This is easily achieved by
holding the connector being inserted in the correct orientation. It's very
easy to insert a DB-style connector without risk of a short. (Having said
that, I've probably shorted more serial pins than I've had hot breakfasts. I
frequently grope with serial connections I can't see at the back of PCs, and
deliberately short pins - sometimes clumsily - for testing purposes.)

 - if the device being attached is mains powered, consider disconnecting it
before attaching. This typically shouldn't be necessary in a domestic
environment. (This isn't specifically to avoid attaching a powered device,
it's intended to avoid the risk of attaching a device which has developed a
large potential difference which could be potentially(!) damaging.
Establishing the serial connection while the device is unplugged from the
mains - which is where the risk of potential difference is likely to
originate - ensures that the 'common' or 'ground' connection is be
established first. Again, having said that, I'm not aware of having
witnessed an actual instance of this.)

The other possible stumbling block to exchanging serial devices on a live
system is having a program running which holds the port open and/or expects
a particular device to be present. I'm struggling to think of a case where
this can't be controlled, either by some kind of configuration option, or by
shutting down the application in question.

Finally, as an alternative to a pure usb-serial adapter, I have been using a
USB hub which also features a serial and a parallel port. I have no idea how
readily available these might be now (since modern PCs seem to have an
abundance of USB ports) but if you can find one it'll probably be quite
cheap. This one has proven very useful for me.

Wayne

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