USB to Serial adaptor

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Does anybody have a favorite USB to RS-232 adaptor that they can recommend?  
Evidently some are not created equal and have had some issues.

A colleague in France reported that he had found some discrepancies in how  
the grounding was accomplished:
  "It appears that the RS232 plug body is NOT always bound to USB plug body,  
nor to the pin 5 (ground) of the rs232 plug,
so that finally there is not the same ground reference between the PC, the  
RS232/USB plugs and then the RS-232 peripheral.
This is the origin of MANY communication errors."

In his case, the adaptor was run on a laptop that had no connection to  
earth. The RS-232 peripheral (which we produce) was earthed.

tia - Oppie  


Re: USB to Serial adaptor
I have a Kingwin adapter cable:

- USB shield connects to braided cable shield.
- Not sure if cable shield goes anywhere at the other end.  No apparent  
electrical connection.
- Pin 5: < 1.3 ohms to USB ground pin (I measure ~0 ohms to computer  
chassis once plugged in).


Tim

--  
Seven Transistor Labs
Electrical Engineering Consultation
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Re: USB to Serial adaptor
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- DE-9 shield not connected.
- Voltage levels meet RS-232 requirements: symmetrical (+/-) 6-7V, with  
some ripple from the charge pump evident.  Not good for a really long  
cable (where the original +/-15V would be better suited), but certainly  
legitimate, not some phony +3/-0V "compatible" interface.

Chip is Prolific (probably PL2303), which has TTL/LVCMOS interface.  Don't  
know what RS-232 driver was used; probably a MAXx232 clone.

- Works well in my limited experiments; seems to have sufficient baud rate  
precision and selection range.  Doesn't seem to transmit frames  
continuously, but that may be a limitation of the program's sending  
capability, or the drivers or USB.  Does correctly recieve continuous  
frames (i.e., complete stop bit immediately followed by a start bit).

Tim

--  
Seven Transistor Labs
Electrical Engineering Consultation
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Re: USB to Serial adaptor

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We've been using these under WIN7, works on XP.
http://www.usconverters.com/index.php?main_page=product_info&cPath67%&products_id32%5

The DB9 shell is floating. Pin 5 is connected to the USB shell.
I have yet to discover a problem with them.  
The USB cable is 3 feet long to boot.

Cheers

Re: USB to Serial adaptor
On Wednesday, October 9, 2013 1:09:06 PM UTC-7, Oppie wrote:
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I've always liked the Keyspan adapters; the single USA-19 works well
and the dual USA-28 (Macintosh style connections) has full-differential
transceivers (RS-422) and works at impressively high data rates (I've
tested up to 240 k baud, it claims 1 M bps).

Re: USB to Serial adaptor
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As a general issue, I prefer the ones which use the FTDI chipsets.
The Linux and Windows drivers both seem to be good, and the FTDI chips
include unique device IDs masked into the chips that the drivers can
use to properly distinguish one  

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As I understand it and read the specs, all properly-defined RS-232
interfaces should be looking at the voltages between the signal lines,
and the "common ground" (pin 5 on a DE-9 per TIA-574).

I don't believe it's proper for a device to depend on there being any
particular connection to the DE-9 metal shell - this may be connected
to the host device's chassis ground, or to the "protective ground"
RS-232 signal (pin 7 on a DB-25, not defined on a DB-9), or to nothing
at all.  On a DB-25 serial connection, pints 1 and 7 (signal ground
and protective ground) are often connected together but this isn't
required.

With RS-232, you cannot depend on their being a common chassis-ground
reference between the two devices at either end of the line.  They may
be quite some distance apart physically, may be powered from different
AC mains, and there may be significant ground currents between the
two.  It's even possible for one or the other to be deliberately
isolated from ground, for safety reasons, or to be powered like a
laptop through an adapter which doesn't carry the building safety
ground through to the device.

If you've got some sort of terminal device which won't work correctly
with even a simple three-wire connection (TxD, RxD, and common
ground), then I'd say that the device is probably at fault, and not
the USB-to-serial dongle.




Re: USB to Serial adaptor
On 09/10/2013 22:50, David Platt wrote:

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I would avoid FTDI parts like the plague.  Often, they work well.

Cheers
--  
Syd

Re: USB to Serial adaptor
On 10/9/2013 3:26 PM, Syd Rumpo wrote:
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I go out of my way to use FTDI chipsets. I never had an issue with them.




Re: USB to Serial adaptor
On 11/10/2013 05:21, miso wrote:
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Nor did I for years.  Now I do: their support is poor and (at least some  
of) their parts are borderline.

Cheers
--  
Syd

Re: USB to Serial adaptor
On 10/11/2013 1:42 AM, Syd Rumpo wrote:
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Care to elaborate?  I have used both Prolific chips and FTDI and never  
had a problem with either.  What problems did you find?  Which parts are  
"boarderline"?

--  

Rick

Re: USB to Serial adaptor
On 11/10/2013 08:52, rickman wrote:
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Specifically the M232R module.  It works.  New PCB with minor changes to  
unrelated circuitry, it dosen't work - 'not recognised' says the PC.  
Often but not always.  Different PC's much the same, different modules  
have differing failure rates.  Oh look, here's an addendum to the data  
sheet, well hidden.  Still doesn't work all the time.

I'd used their parts for years, but as soon as I had this problem I  
discovered that I wasn't alone.  If I disable the 40MHz clock on the  
host PCB, USB module works, always.  The clock doesn't go near the  
module, the power looks clean.

I dare say we'll get it working, but it seems to be very sensitive to  
something.  Phases of the moon, probably.


Cheers
--  
Syd

Re: USB to Serial adaptor
On 10/12/2013 8:10 AM, Syd Rumpo wrote:
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But that isn't a converter the end user will buy. It seems to be an  
unrelated issue.


Re: USB to Serial adaptor

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Yep.  Anything with an FTDI chip.  I'm forced to deal with ancient
Motorola radio programming software that talks directly to the serial
UART.  Without a proper emulator, the Motorola software just doesn't
work.  I've done battle with a small assortment of USB to serial
cables using Prolific, TI, and SiLabs.  Each will work with some
combination of computah and radio, but only the FTDI chip seems to
work with all combinations.

I recently purchased several of these:
<http://www.ebay.com/itm/370761532032
Of course, the drivers on the CD were somewhat out of date, but that
was easily fixed with a download from the FTDI web pile:
<http://www.ftdichip.com/Drivers/VCP.htm

Note:  I'm using DOSbox to slow down the computer so that the old
Motorola software will run.  That doesn't work with Prolific cables
but works fine with FTDI.

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: USB to Serial adaptor
On 10/9/2013 8:41 PM, Jeff Liebermann wrote:
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Ditto this. I use FTDI with old serial radios. They work fine.

Prolific is probably second best. But I have had issue with them as OSs  
changed. FTDI keeps the drivers up to date for old products. That is a  
rarity these days.


Re: USB to Serial adaptor

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The current head scratcher is that the Maxtrac software won't run on
anything faster than a 486, yet I have a Panasonic CF-25, with a
Pentium 166 that runs it just fine.  No clue why (yet).

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The problem with Prolific adapters are counterfeit chips.
<http://www.eevblog.com/forum/reviews/note-how-to-not-get-scammed-with-prolific-%28pl2303%29-usb-serial-adapters/
I bought about 6 different USB to serial adapters on eBay for about
$2.50/ea from a mix of vendors.  I was trying to find an adapter that
would work reliably with DOSbox and MoSlo.  The included drivers would
install, but if I used the drivers from the Prolific web pile, it
would refuse to recognize the adapter.  That's intentional as Prolific
is defending itself against counterfeits.  Of course, *ALL* the
adapters I bought on eBay were counterfeit, which should offer a clue
as to the extent of the problem.  Caveat emptor.

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: USB to Serial adaptor
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So, what were you expecting? ;-)

...Did any of the adapters have brand names on them, or were they all  
assorted POS-1 specials as the price and source suggest?

I note my Kingwin doesn't actually have a label on it, but it was from a  
reputable distributor.

Tim

--  
Seven Transistor Labs
Electrical Engineering Consultation
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Re: USB to Serial adaptor
On Fri, 11 Oct 2013 15:39:13 -0500, "Tim Williams"

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Actually, it was a desperation move on my part.  I needed something to
program the old radios.  Everything I had was too fast for the old
software.  All my old 486 laptops were not functional.  DOSbox ran the
Motorola software, but none of my laptops have built in serial ports.
So, I was desperate for a USB to serial adapter that would work with
DOSbox.  In desperation, I thought that my collection of adapters
(mostly Prolific chips) were defective and that all I need to do is
buy one that worked.  So, I ordered an assortment on eBay, picking
devices that looked different from each other.  I never considered the
possibility that they were all counterfeit and would all use the same
counterfeit chip.  After that failed, I ordered a cable with an FTDI
chip, which worked.

Note:  DOSbox and the Motorola sortware ran nicely on several desktops
that had serial ports.  However, I needed a laptop as I wasn't going
to drag the desktop and monitor to a mountain top.

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The pile is in my office so I can't check for a few days.  The one I
have in my laptop bag is translucent blue and has no name on it.

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Point taken.  It's best to buy from someone with a clue.  Yet, I've
purchased counterfeit RAM, SD memory, Jetdirect cards, and batteries
from what might be considered reputable vendors, so that's no
guarantee of success.

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: USB to Serial adaptor
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Interesting.. I bought 10 USB to TTL serial adapters for about the same
price.  These have just GND, Tx and Rx brought to loose single pin headers.  
They all worked fine with the latest Prolific software: PL2303HXD chip
detected.  (Perhaps the counterfeiting has caught up...).

BTW, I've given up using DB-9s for enclosureless designs.  It's only a tiny
bit more to buy and include a $2.50 cable and provide a 6-pin "arduino"
header than to provide MAX232, caps, and DB-9 connector.

These were for a personal project:
    http://relaysbc.sourceforge.net/serial.html

Someone needs make a standard for an external TTL serial connector.

Here's another consideration: I recently specified a 9 ft. USB to DB-9
RS-232 serial adapter for an appliance we make.  This kind has the board in
a bump in the middle of the wire, not built into the connectors.  Now where
is the best place for the bump? In the old days I would say put it on the
USB side since slow speed RS-232 can go quite a long distance.  However,
standard testing will include 921600 baud... so it's better to put it on the
DB-9 side and use the USB 1.1 max cable length.

--  
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Re: USB to Serial adaptor
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Turbo Pascal "Division by zero" ?


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?? 100% natural


Re: USB to Serial adaptor

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No, although I've also seen that trying to run some of my old compiled
Borland software.  In this case, the Maxtrac programming software just
hangs when run.  Sometimes, I can hit a few function keys to change
menus, but eventually, it hangs.  Even worse is that the DOS (cmd)
window will not close and the machine needs to be rebooted.  There is
software that's been around for many years that attempts to solve the
problem:
<http://www.hpaa.com/moslo/
<http://en.wikipedia.org/wiki/Slowdown_utility
I bought MoSlo but couldn't make it work reliably.  Then came DOSbox,
which has a similar purpose, but works MUCH better:
<http://www.dosbox.com
So far, it has run all my old 1980's software and most of the old
Motorola programming software that I've tried (Maxtrac, Syntor 9000,
GM300, GP300, GP350, GTX, HT600, HT1000, MSF5000, etc) with a standard
serial port.  However, I was stuck with the USB to serial adapter
problem, until I switched to an FTDI based adapter.  Also, I have a
customer that is stuck with ancient DOS software (Foxplus, dBaseIII,
and Telemagic) that crashes on fast machines.  I've been using a
various slow down utilities and tricks, but DOSbox works much better.
Telemagic runs an external modem telephone dialer, which I couldn't
make work using the (counterfeit) Prolific adapters, but which might
work with the FTDI adapter.  However, the real benefit is that I can
now safely recycle all the old junk laptops I have laying around the
office.

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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