[ale] [Slightly OT] Prolific

[Ron Frazier (ALE)]

David Tomaschik <david at systemoverlord.com> wrote:

>On Sun, Nov 4, 2012 at 4:31 PM, mike at trausch.us <mike at trausch.us>
>wrote:
>> On 11/04/2012 07:12 PM, Sam Rakowski wrote:
>>>
>>> I've a PL2303 based serial cable that has worked fine for me, on the
>>> off chances when I get to use it.
>>
>>
>> Interesting.
>>
>> I must be sorely unlucky.  :)
>>
>> This one that I bought from fry's the other day doesn't work with
>Linux,
>> doesn't work with Windows, and spams the kernel ring buffer with all
>sorts
>> of error messages.
>>
>> If it were the first prolific device I ever bought, I'd assume it was
>> defective.
>>
>> I bought a parallel cable ages ago (actually, I bought like six of
>them,
>> from various places, because I was stupidly frustrated).  I even went
>with
>> different brands, only to find out that they were all built around
>the same
>> stupid Prolific chipset.  The problem with them all was the same:  
>Whenever
>> I would send a print job to the printer, the printer would seemingly
>do
>> nothing.  I could then try to cat things to the printer, which would
>simply
>> hang.  By some strange turn of events, I realized that if I pressed
>the
>> printers ON LINE button twice, to bring it offline and then back
>online, the
>> printer would start printing the stuff I sent to it, but the first
>byte
>> would be missing from the stream.
>>
>> Given the popularity of some of the brands (Belkin, for example, was
>one of
>> them), I thought that it must surely be a bug in the Linux kernel.
>So, I
>> tried in Windows.  Same problem.  Printer?  No, it worked with a real
>> parallel port, and a parallel-port inkjet wouldn't print at all (no
>way to
>> toggle the ONLINE pin).
>>
>> Greg KH, a kernel dev, has apparently been getting bad reports about
>> Prolific hardware for a long time.  Anymore it seems that if someone
>comes
>> to linux-usb to whine about it not working, he says "go get a real
>piece of
>> hardware from FTDI".
>>
>> I wonder why they're such a problem.
>>
>> I wonder why yours actually works.
>>
>> And yes, I tested this cable with a Windows laptop.
>>
>> RING
>>
>> RING
>>
>> comes in, but nothing ever gets out... bits can check in any time
>they like,
>> but they can never leave...
>>
>>
>>         --- Mike
>
>I have a PL2303-based cable that I routinely use with a router and it
>works fine.  I've never even seen a cable based on FTDI that was
>marketed for USB to standard serial, only ones for microcontroller
>"serial".

Perhaps you could do some testing with two usb / serial cables connected to each other with a null modem adapter in the middle.  You could have two scripts running, one which feeds data to one port and the other which reads data from the other port and compares the results.

In the earlier part of 2012, I was doing experiments with building my own NTP server with a serial I/O GPS.  I'm pretty sure I had a Prolific usb / serial cable working fine both in Windows and Linux.

Sincerely,

Ron



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Ron Frazier
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