USB to Serial adaptor

[Oppie]

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

 

[Tim Williams]

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

 

[Tim Williams]

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).

- 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

 

[Martin Riddle]

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

We've been using these under WIN7, works on XP.
http://www.usconverters.com/index.php?main_page=product_info&cPath=67&products_id=325

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

 

[whit3rd]

Does anybody have a favorite USB to RS-232 adaptor that they can recommend?

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).

 

[Syd Rumpo]

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

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

Cheers

 

[Klaus Kragelund]

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.

I have had good experience with this one:

http://www.amazon.com/MCT-U232-P9-Adapter-Certified-XP-Windows7/dp/B004V89JMC

Cheers

Klaus

PS Some USB to serial converters do not have good control of the handshake lines, so the f*'' up the timing. AFAIR the MCT behaved well

 

[Oppie]

Many thanks for all the replies.

My colleague shared that these seem to work in his application
http://www.startech.com/Cards-Adapt...s/USB-RS232-DB9-Serial-Adapter-Cable~ICUSB232
http://www.startech.com/Cards-Adapt...-RS232-DB9-Serial-Cable-Male-Male~ICUSB232SM3
http://www.startech.com/Cards-Adapters/Serial-Cards-Adapters/4-Port-USB-to-RS232-Adapter~ICUSB2324...

While these did not
http://www.startech.com/Cards-Adapt...ters/2-Port-USB-RS232-Serial-Cable~ICUSB2322F
http://www.startech.com/Cards-Adapt...o-RS-232-2-Port-Serial-DB9-Adapter~ICUSB232C2

Still sorting out the whys and wherefores...

 

[Cydrome Leader]

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

This is the only model I found that works correctly with any equipment
that's not broken:

http://www.digi.com/products/model?mid=207

expensive yes, but worth it.

 

[Martin Riddle]

Many thanks for all the replies.

My colleague shared that these seem to work in his application
http://www.startech.com/Cards-Adapt...s/USB-RS232-DB9-Serial-Adapter-Cable~ICUSB232
http://www.startech.com/Cards-Adapt...-RS232-DB9-Serial-Cable-Male-Male~ICUSB232SM3
http://www.startech.com/Cards-Adapters/Serial-Cards-Adapters/4-Port-USB-to-RS232-Adapter~ICUSB2324...

While these did not
http://www.startech.com/Cards-Adapt...ters/2-Port-USB-RS232-Serial-Cable~ICUSB2322F
http://www.startech.com/Cards-Adapt...o-RS-232-2-Port-Serial-DB9-Adapter~ICUSB232C2

Still sorting out the whys and wherefores...

USB is pretty sensitive to ground bounce. We've wiped out usb ports
because of that. The shorter usb converters may work because they are
less sensitive to noise due to the short cable length (one has the
chip in the USB connector end, the other is 12" long). As for the 4
port powered hub, might be the power supply is robust and external.

I wonder if a usb isolator will make the longer cables work.

Cheers

 

[miso]

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

Cheers

I go out of my way to use FTDI chipsets. I never had an issue with them.

 

[miso]

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.

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.

 

[miso]

Make sure the driver is up to date on

http://www.startech.com/Cards-Adapt...ters/2-Port-USB-RS232-Serial-Cable~ICUSB2322F

This is a FTDI chipset device, so it should be good.

 

[Syd Rumpo]

I go out of my way to use FTDI chipsets. I never had an issue with them.

Nor did I for years. Now I do: their support is poor and (at least some
of) their parts are borderline.

Cheers

 

[rickman]

Nor did I for years. Now I do: their support is poor and (at least some
of) their parts are borderline.

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"?

 

[rickman]

I have had good experience with this one:

http://www.amazon.com/MCT-U232-P9-Adapter-Certified-XP-Windows7/dp/B004V89JMC

Cheers

Klaus

PS Some USB to serial converters do not have good control of the handshake lines, so the f*'' up the timing. AFAIR the MCT behaved well

I have to be at least a little suspicious of these sellers.

"This is an Industrial Grade Product using a Philips FTDI Chip Set."

Since when was Philips involved with FTDI??? Oh yeah, since when was
$30 a "low" price for a USB serial interface? FTDI chips are used in a
many, many products at a much lower price, often under $10.

 

[Tim Williams]

I bought about 6 different USB to serial adapters on eBay for about
$2.50/ea from a mix of vendors.
<snip>

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

 

[Syd Rumpo]

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"?

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

 

[Jasen Betts]

The current head scratcher is that the Maxtrac software won't run on
anything faster than a 486,

Turbo Pascal "Division by zero" ?

 

[Charlie E.]

I have been trying to find a good USB to RS485 serial adapter. I have
a small contract to modify some code to add MODBUS capability to a
product. I found one item on Amazon that had USB to serial
TTL/RS232/RS485 that really fit the bill, so I got one.

It came in, and seemed to work, then just kinda stopped. I think it
is that TTL capability - makes the whole thing really static
sensitive! I ordered another one, and today right in the middle of
testing, it has gone bad as well. All my commands suddenly started
failing CRC. After spending all day (on a Saturday!) trying to 'fix'
my code, I finally pulled out my old USB to RS232 dongle, and my code
is fine! Not a fun way to spend a weekend, especially since my
customer is supposed to demo the MODBUS capability to the customer on
Monday!

Well, at least on RS232 it works fine...