Re: Re: RS232/482 Qs

[Harry Broomhall <haeb@xxxxxxx>]

On Sat, 11 May 2002 12:45:05 -0000, you wrote:

>The maximum cable length in the spec. is 50ft, but this is specified
>for 20kBaud. Given that the spec. was written in 1967, and technology
>has marched on, you will be able to achieve *considerably* longer 
>distances at 9k6 - 50m should be readily achievable, 100m quite 
>possible, with the limiting factor being the cable's capacitance (low
>capacitance is good) and, to a lesser extent, resistance (low 
>resistance is good).
>
>Note that these figures are for RS232, not RS232C. RS232C uses TTL 
>(+/- 5V level signals), as opposed to +/- 12V signals used by RS232
>proper, which offers much greater noise immunity and are therefore 
>able to cover much greater distances. 
>

   Er - not quite.  In RS232C the 'C' indicates a revision
of the
original standard.  In this case 'C' was a revision of 'B'.  It's
just
that the 'C' revision was around so long most people lost sight of
this!

   I *believe* (but I'd need to go and look it up) that the
current
revision is 'F'.  (Later - having checked - this is correct:
http://www.tiaonline.org/standards/search_results2.cfm?document_no=TIA/EIA-232-F
)

   As regards to the voltage - RS232C said nothing about TTL
levels.

The voltages specified are the same as they always have been:

Open cct voltage to be under 25V
lowest mark or space +- 3V.
normal operating voltage - between 5 to 15V

   Regards,
           Harry.

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