[OpenIndiana-discuss] stty source code

Roel_D openindiana at out-side.nl
Thu Sep 6 19:04:10 UTC 2012

I only buy new laptops with building rs232 ports, like the HP 6550b I own. 
I wasted too much time on crappy USB convertors. 

-----Original Message-----
From: James Carlson [mailto:carlsonj at workingcode.com] 
Sent: donderdag 6 september 2012 20:46
To: Discussion list for OpenIndiana
Subject: Re: [OpenIndiana-discuss] stty source code

Roel_D wrote:
> "never" use USB-> Serial when you're testing something. There is a 
> huge difference between products, and the bad products behave very
> Don't forget that the voltage of USB is 5V MAXIMUM but can be much 
> lower depending on the hardware, legacy serialports need a good 5V for 
> a logical 1.
> So communication can be disrupted by voltagedrops because the logical 
> 1's are not transmitted at the right voltage.

Good devices have a charge pump to get the standard +/- 12VDC, such as the
MAX232 or SP213.  It wouldn't be too surprising to find "cheap"
designs that lack the charge pump.  :-<

However, you are certainly right that USB serial adapters are in general all
too often substantially less than ideal.  In my experience, it's due to the
layers of software between the actual bits on the wire and the interface
exposed to the application.  If you can get a real serial port (often not
included in modern hardware, but usually available on an adapter board),
you're far, far better off using that.

(Yeah, I'm trying to be charitable with that ...)

James Carlson         42.703N 71.076W         <carlsonj at workingcode.com>

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