[time-nuts] TBOLT communication

[Ulrich Bangert]

Predrag,

I had always thought that Recommended Standard 232 calls the region from
-3 to +3 volts a "disallowed state" and suggests to use at least +/- 5 V
levels so that +/- 6 V should be absolutely conform with RS232.
Fortunately - or unfortunately ? - all modern RS232 receiver chips have
a built-in fail-safe state which makes their TTL outputs go high with no
RS232 input signal connected. Some people abuse this property in that
they drive the input with 0 to anything voltage. But I have never seen
such a behaviour in a USB to serial converter. 

Over the last years I had a lot to do with USB to serial converters
because all modern gas analyzers for air pollution measurements have
serial ports while most modern pcs have only USB ports. We have seen
effects of sudden stops in communication with some brands (perhaps due
to driver instability) but we have never had a RS232 voltage level based
problem.

Best regards
Ulrich

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Predrag Dukic
> Gesendet: Mittwoch, 24. September 2008 15:10
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] TBOLT communication
> 
> 
> 
> 
> I had the same problem with some other devices, and I took apart 
> several converters.
> Most of them were unable to generate sufficient levels for a proper 
> communication with rs232.
> Internal charge pump was generating  +-6V instead of +-12 or +-15 
> that is normal for rs232.
> 
> Putting additional +-12 V source on the psu pins of the converter 
> chip might help.
> 
> 
> Predrag Dukic
> 
> 
> 
> 
> At 10:58 24.9.2008, you wrote:
> >Hi,
> >I have just spent a week or two trying to talk to a Trimble 
> >Thunderbolt. I have a laptop running VISTA, about which 
> there is little 
> >to say. The laptop has no serial ports, but I have some USB/Serial 
> >converters that successfully run my HP 3815A and a Samsung 
> GCRU/D, and 
> >also communicate with my HOBO loggers.
> >The USB/Serial converters are a little difficult to use, sometimes
> >hanging, necessitating
> >unplugging and plugging back in. They get assigned to various Port
> >numbers but tend to keep
> >the same number from day to day. The ports can be configured in the
> >management function.
> >However the TBOLT refuses to talk to the converter, to the extent
> >that I thought that I must have
> >damaged the TBOLT.
> >Today, as a last resort, I remembered an old PC, dragged it out and
> >stoked it up, and to my delight
> >the TBOLT monitoring program ran without difficulty under Windows
> >2000 with a conventional serial port.
> >Now I vaguely remember talk about RS232 communications and the need
> >for pull up or down
> >resistors and supplies, but searching the archives I could find
> >nothing relevant.
> >Can anyone tell me how I could run the TBOLT off a 
> USB/Serial converter?
> >cheers, Neville Michie
> >
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