[ale] [Slightly OT] Prolific

[Michael H. Warfield]

On Sun, 2012-11-04 at 19:10 -0500, mike at trausch.us wrote:
> Just out of curiosity, has anyone here actually seen a WORKING chip from 
> Prolific?

I have stacks of them.  No problem...  They are the heart of most of my
remote maintenance systems with serial consoles.

> I'm finding myself wondering how the hell they're still in business. 
> Every USB cable I have purchased that has a PL* chip in it simply 
> doesn't work.  Doesn't matter if we're talking about serial or parallel 
> interfaces, they just never ever work.

> And of course, you can never tell what chipset is in the stupid things 
> until you've bought them and hooked them up and then you have that 
> "D'oh!" moment.

> Seems that Fry's only carries such cables, so I guess I won't be buying 
> from there anymore.  Linux kernel devs strongly suggest avoiding them.

> The problem this time?  It will receive data from a modem, but not 
> transmit to the modem.  So I can see:

> RING

> RING

> But if I try to send "ATA" nothing happens, no echo, no going off-hook, 
> no screeching, no nothing.

Oh, I recognize this problem.  I've seen it many times in the past.
It's a hardware flow control problem.  Something is hosed in your RTS /
CTS (Request to Send and Clear to Send) or DTR / DSR (Data Terminal
Ready / Data Set Ready) signal wiring and configuring.

Most often, for me, this has been RTS / CTS in a cross over cable where
you have two choices.  The simple choice is to loop the CTS on one side
back to the RTS on the same side basically disabling the hardware flow
control.  The PROPER way to do it is the connect the RTS on one side to
the CTS on the other side but, then, both sides have to be configured
for full hardware flow control or both have to be configure to ignore
CTS/RTS hardware flow control.

You have to have your hardware (RS-232 signaling lines) match your
software for the UARTS for flow control matching.  What you are
describing is exactly the failure I see when this is not the case.
 
> Wonderful, yes?

> SO anyway, just curious: has anyone heard of a chip from this 
> manufacturer actually performing as intended, or do they just hate me?

Bottom line - it's not the chip.  It's your interconnect wiring and flow
control setup.

> 	--- Mike
> 
> -- 
> A man who reasons deliberately, manages it better after studying Logic
> than he could before, if he is sincere about it and has common sense.
>                                     --- Carveth Read, “Logic”

Regards,
Mike
-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
 PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!
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