Strange RS232 Wiring

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Costas Vlachos 21 years ago

Not exactly a design question, but I thought some of you may be able to help. I've just bought a USB-to-RS232 converter cable for my laptop and it came with a weird 9-pin FEMALE to 9-pin MALE adapter. I initially thought it was a null-modem adapter, but upon examination it uses the following wiring which I've never seen before:

FEMALE MALE

PIN 1 o----+ +---------o PIN 1 | | PIN 2 o--- | ---+ | PIN 2 | | | PIN 3 o--- | -- | ---+ | PIN 3 | | | | PIN 4 o--- | -- | -- | ---+ PIN 4 | | | | PIN 5 o--- | -- | -- | -- | ---+ PIN 5 | | | | | PIN 6 o----+ | +--------------o PIN 6 | | | PIN 7 | | +----o PIN 7 | | PIN 8 o-------- | --------+ PIN 8 | PIN 9 +-------------------o PIN 9

CASE o-----------------------------o CASE

Note that pins 2 and 3 (TxD, RxD) are not used at all in the MALE side! The adapter has the label "NBT/BT" on it. There is no mention about it in the box or manual. I Googled about it but nothing relevant came up... Any ideas on what this wiring is for?

Many thanks.

Costas _________________________________________________ Costas Vlachos Email: snipped-for-privacy@hot-X-mail.com SPAM-TRAPPED: Please remove "-X-" before replying

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Tim Wescott 21 years ago

It looks like they got a connector mirrored on their board, then fixed it with the weird connector rather than pitching the stuff and starting over again.

Tim Wescott Wescott Design Services http://www.wescottdesign.com

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Si Ballenger 21 years ago

I bought several adapters like below cheap and they don't work as far as I can tell. The incorrect connector should have a warning sign. The CD that comes with it looks somewhat homemade. I've got another adapter that looks similar but with the correct connector and it works great. Beware of the type below with the attach screws!

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Costas Vlachos 21 years ago

I had a similar experience. I bought one like in your picture from eBay and it didn't work. Was recognised by the system as a COM port, but there were no signals coming out of the serial connector! I contacted the seller who then sent me a different one which looks similar but without the thumb screws. This one works perfectly with no problems at all. As to the purpose of the "NBT/BT" adapter that came with it (wiring in my original message), I still don't know what it's for. The cable works fine without it.

Regards, Costas _________________________________________________ Costas Vlachos Email: c-X-vlachos@hot-X-mail.com SPAM-TRAPPED: Please remove "-X-" before replying

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Si Ballenger 21 years ago

Same here, no signal on the tx line. Bought it from

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Below is the type that works well.

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Mark Haase 21 years ago

Haha, I too bought a suspicously similar looking USB->RS-232 cable. Mine worked intermittently but only with certain devices. I shelved it.

|\/| /| |2 |< mehaase(at)sas(dot)upenn(dot)edu

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Carl D. Smith 21 years ago

Maybe the mystery connector fixes the bad USB->Serial adapter that has no signals on the tx/rx?

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Doug McLaren 21 years ago

| Same here, no signal on the tx line. Bought it from |

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Below is the type that works well. | |

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$1 each, $10 shipping. Bah! Why can't they just say $10 each, $1 shipping and be honest about it?

Do you know if Linux supports these?

Anybody know of an inexpensive USB to multiple serial ports (2 or 4 I guess) device? (Yes, I know a hub and four of these things would work too.)

Doug McLaren, dougmc@frenzy.com "I can explain it for you, but I can't understand it for you." -Anon.

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Costas Vlachos 21 years ago

Yes, I thought that too and tried it with the faulty cable, but still no joy... The mystery connector looks like a hand-made thing, with loose cables soldered to the male/female ends, in a generic snap-on grey casing with a small "NBT/BT" sticker on it. Weird stuff...

-- Regards, Costas _________________________________________________ Costas Vlachos Email: snipped-for-privacy@hot-X-mail.com SPAM-TRAPPED: Please remove "-X-" before replying

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Si Ballenger 21 years ago

Still better than $12-15 plus $8 postage from the low price retailer

Apparently so. the below is included on the driver disk along with windows and mac. It is by Prolific.

Release Information

Driver Version for Linux 2.4.x : V0213

Released date: 02/13/2002

Files Included in This Release: pl2303.c pl2303.h usbserial.c usb-serial.h readme.txt makefile Changes in This Release: 1. To fixed using cat command problem in Linux

Search ebay for the Edgeport 4 and 8 port serial usb adapters. Reported to be an excellant product made by IONetworks (search google).

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Fred Bloggs 21 years ago

BT means Bluetooth and NBT is non-Bluetooth, for the burgeoning serial-bluetooth backfit market. (I think.)

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Strange RS232 Wiring

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