# USB Serial PL2303 Problem

## onslo

Hi there,

I'm new to Gentoo, and reasonalbly new to Linux in general, though that's not to say that I am a complete n00b  :Wink: 

I recently purchased a USB-Serial adapater that uses the PL2303 Prolific Chipset. The reason being that I need to increase the number of available serial ports on a system for a very small cost. USB-Serial appears to be the best method for this. However......

I am having a problem getting bidirectional comms working between the two serial endpoints.

I have the PL2303 plugged into one of the usb ports on my Gentoo box (vanilla 2.4.27 at present). This creates a /dev/usb/tts/0 device.

I am then using a 3 wire, null-modem cable to connect to either a win2k box running hyperterminal or just one of the other real serial ports on the same Gentoo machine, thus...........

```

Gentoo Minicom                                        Win2K Hyperterm

/dev/usb/tts/0  ----------Null Modem Cable-----------  com1

```

Now, when I type anything on the Win2K Hyperterminal session I do see those characters being outputted on the Gentoo Minicom session. However, the same cannot be said if I reverse the procedure. I do not see any output in the Hyperterminal session when typing into the Gentoo Minicom session.

In fact, I only seem to be able to get one way comms using this adapter and Linux (have tried various Debian kernels too). It does not seem to be possible to get bidirectional comms working.

I have checked the obvious, and the not so obvious, such as permission setting on the /dev/usb/tts/0 port, using different kernel versions, using different USB cards, using totally different PC hardware, checking cable pinouts, checking that the adapter does actually work (works fine under Win2K). I have even shorted the CTS/CRS and DTS/DRS/DCE serial lines together at the PL2303 end to see if spoofing the handshaking would work, but alas I am still no further down the road than before.

Is it possible that Hotplug is having an effect? Or does anybody have any other ideas or suggestions that might help ?

Many thanks for your time....

Regards

Onslo

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## onslo

I'm going to try another adpater to see if that resolves the problem, but I don't think that it will unless it's a totally different chipset.

In the mean time if anybody has any suggestions what-so-ever then please do not hesitate   :Wink: 

Regards

Onslo

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## forbjok

 *onslo wrote:*   

> I'm going to try another adpater to see if that resolves the problem, but I don't think that it will unless it's a totally different chipset.
> 
> In the mean time if anybody has any suggestions what-so-ever then please do not hesitate  
> 
> Regards
> ...

 

Did you try using the 'cu' utility that comes with the taylor-uucp package instead? I used minicom before, and found it to be very inconsistent and unstable.

I believe the syntax is something like this:

```
$ cu -l /dev/ttyS0 -s 9600
```

(substituting device and baud rate with appropriate ones)

btw. I don't have a usb-serial converter, but I'm planning to buy one.

----------

## onslo

Thanks for the reply....

I don't have the taylor-uucp package emerged i'm afraid, but I have made some progress...

I managed to get my hands on an FTDI adapter, which when plugged in is recognised by the system. This appears to work exactly as expected.

If I connect one end to a Win2K hyperterminal session and the other through the FTDI adapter (/dev/usb/tts/0) to my Gentoo box I can communicate both ways...

cat filename > /dev/usb/tts/0   (the contents of filename is seen on the hyperterminal session)

cat /dev/usb/tts/0    (whatever I type on the hyperterminal session appears on the Gentoo box)

Minicom freaks out a bit, but hey, that's just minicom and I don't intend to use that anyway.

So I am happy that the FTDI adapater works properly, and am now convinced that there is something amiss with the PL2303 adapter support under Linux.

The only problem with this is that the PL2303 adapter is considerably cheaper than the FTDI adapter, but then I guess you could say that it's only cheap if it actually works properly.

Has anyone else had any success with PL2303 and Linux, especially bidirectional comms ?

Regards

Onslo

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## forbjok

What brand/model are the 2 USB-Serial converters?

Just curious, as I'm planning to buy one, and want to know if there are any particulars I should look for, or avoid  :Wink: 

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## onslo

The adapter that appears to work properly is a VSCom USB-Com adapter : 

http://www.vscom.de/produkte/vscom_usb-com.html

The adapter that only seems to allow one-way communications is this one : 

http://www.ebuyer.com/customer/products/index.html?action=c2hvd19wcm9kdWN0X292ZXJ2aWV3&product_uid=40608

Regards

Onslo

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## forbjok

Okay, thanks  :Very Happy: 

I'll stay away from Ebuyer then  :Smile: 

By the way, did you try it on window? Just wondering, cause if not, it could also be faulty hardware.

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## onslo

Yeah, I proved that the hardware works fine on Windows (Win2K Pro SP4).

Am certain it's a driver issue within Linux for the PL2303.

Regards

Onslo

----------

