Re: Using USB instead of RS232 on embeded project
From: Paul Carpenter (paul$_at_pcserv.demon.co.uk)
Date: Fri, 24 Sep 2004 23:20:34 +0100 (BST)
On Friday, in article <ocX4d.356878$sh.333765@fed1read06>
email@example.com "Mike Turco" wrote:
>"Paul Carpenter" <firstname.lastname@example.org> wrote
>>>like easysync.co.uk - using FTDI - are fixing the laptop problem, so why
>>>change unless it's a hard marketing requirement?
>> Should read "follow the current desktop fad".
>Finding laptops with a serial port has always been difficult, much less
>finding a laptop with two serial ports if that's what you need. Multiple
PCMCIA or USB to RS232 exist and have existed for some time.
>serial ports have always been a problem with desktops, too, if you need more
Multiple port PCI cards and before that ISA cards have existed and are
>than the two that come with the machine. (I'm speaking of situations where
>people used to need multiple serial-based products on their machines in
>commercial and industrial applications, not hobbyist setups or VAR systems.)
So am I, even years before the PC, industrial applications often had add in
cards of multiple serial ports.
>Now, there is USB. Virtually all computers have it, and have had for at
>least a few years now. Need to hook up more stuff? No problem, get a hub.
>You can even pull power from the USB port, not much, but its there and a lot
>of times you can use it.
>Hey, I miss serial communications too. It was easy to deal with, even in
>asm. USB definitely ads a level of complexity. But times have changed, and
>USB is superior to serial for many different types applications.
Now you are in the realms of long term support and conflicts beyond your
control. Having seen too many badly written pieces of USB devices that mean
you are potentially sharing a communications channel with soemthing beyond
Let's see well known brand of scanners that added the following levels
of software as their scanners kept up with the latest fad and they did
a major kludge on their software. The device started as a SCSI device,
became parallel port, then USB, so we ended up with the following drivers
SCSI pseudo device
--- Parallel port to SCSI driver
------ USB to parallel driver
---- various USB drivers to talk to the device
The customer sites I have been to where the systems had to have the multi
interface devices connected by means other than USB, as the USB devices
and their software interacted with each other causing crashes or other
Most of the host side software, like most windows applications assumes
it is the ONLY thing added to a virgin system.
Plug and play is NOT that, but load the software BEFORE connecting the
device. Then make sure you have either shut the machine down or used
"Safely remove Hardware", before disconnecting. The number of people
who I have seen caught out by these is beyond belief.
Then the support nightmares of hardware or operating system upgrades
and there is no longer support for devices. I have seen this already
for USB devices, because the toy market called desktops/laptops assumes
at the slightest problem everything is ditched for the new model.
USB is NOT mature on the software front for me to consider for many
applications, either due to burst communications or random connections
like once a month.
There are PC type applications where USB like interfacing would be a good
idea (cameras, scanners, temporary media connections), but too much is
done on it relying on using up the host resources to do what should be
done in the device. Classic example being inkjet printers.
For PC applications not involving Games, typewriting, web browsing and
other toy usages, USB adds too many non deterministic features to make
>> I wonder how many have had requests to wireless network their current
>> because it would be nice, despite the overkill for many applications.
>Overkill, by who's definition?
There are many applications, where the environment will mean it is not
practical. Excessive addition of cost and/or power consumption for the
amount of benefit. Let alone the complexity of adding to quite a few
applications a 16/32bit processor module to do the work of the wirless
link on an application that is 4/8 bit in the first place.
If you want to have PC fad, make the system from a PC in the first place.
More often the things are added because they can or it is the latest fad
e.g. Bluetooth, or internet access (e.g. washing machines, pens and toaster
that have internet connections).
I have seen too many projects that used a PC that should have been a black
box that was a 100baseT interface for the archiving of data, that have
caused long term support and manufacturing problems due to inability
to get the same PC three months later, let alone the software and
interface cards issues.
-- Paul Carpenter | email@example.com <http://www.pcserviceselectronics.co.uk/> PC Services <http://www.gnuh8.org.uk/> GNU H8 & mailing list info <http://www.badweb.org.uk/> For those web sites you hate