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'Signal loss!?'
1999\05\15@145626 by llgren

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hi there i seem to recall that RS232 transmissions should be done over short
cables. since there are only -3/+3v levels, is this true.

Since this transfer shall travel from 0.3 M - 200M i may need a potent
voltage level and a good shielding.

Which do you think is the best way too boost such a signal, should i boost
it straight from the output pin from the pic, with the help of a NPN
transistor, that drains say.. 12v-24v then convert that level of voltage
back to TTL with a 7805, is the 7805 fast enough? we are after all talking
1200 baud here, i do not seem to find a datasheet that describes this.

Or make some sort of optic transmission, ( which is less cheap ), via optic
cables, the positive side of this is that it wont be affected by
distrubances.

Hit me with some of your experiences in this matter, It would be be most
appreciated.


Greets
Robert

input...input... i need.. input...

1999\05\15@155846 by Markku VenŠlŠinen

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According to the RS-232 standard, it operates at -12/+12 volt signal
levels. Some people do use RS-232 at lower voltages (and short distances),
but I think realistically  5 volts is probably a good minimum. In any case,
the distance you can achieve decreses as you increase the baud rate.

You may want to look at RS-422. The communication protocol is the same as
RS-232, but electrically communication occurs over two 'balanced pairs' of
wire (one pair for receive, and the other pair for transmit). RS-422 is
more noise resistant, and good for much longer distances than RS-232.

A company I worked with several years ago used single 16-pin DIPs to
convert RS-232 <--> RS-422 to allow two RS-232 devices at 9600 baud to be
placed further apart in a building (between two electrical rooms, one on
the 5th floor, the other in the basement). Unfortunately I don't remember
what the chip was or even who makes it, but it was cheap (only about a
dollar in small quantities).

{Quote hidden}

---
Markku VenŠlŠinen
spam_OUTmarkkuvTakeThisOuTspamuniserve.com

1999\05\15@174016 by Jim Paul

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Robert,

I believe that the RS232 standard specifies + and - 12v for the signals.
It's just that to be a true signal, it hacannot fall below the + and - 3
volt
level.  Or is this what you were saying?


Regards,


Jim


{Original Message removed}

1999\05\15@182239 by llgren

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T

1999\05\15@200345 by Lee Jones

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> i seem to recall that RS232 transmissions should be done over
> short cables. since there are only -3/+3v levels, is this true.

Essentially, yes.  EIA/TIA-232 is designed for short distances.
(It was upgraded from a recommended standard, i.e. RS-, to a
full EIA/TIA standard over a decade ago.)

In summary, EIA-232-E specifies the transmiter as +5 to +15 or
-5 to -15 volts.  Receiver state is defined when the circuit is
less than -3 volts or more than +3 volts.

EIA-232-E, section 2.1.3 -- "the signal shall be considered in
the marking (binary 1) state" when the circuit's voltage "is more
negative than -3 volts" and "shall be considered in the spacing
(binary 0) state" when "more positive than +3 volts".  The range
between -3 to +3 volts "is defined as the transition region.  The
signal state is undefined when the voltage" is in this range

EIA-232-E, section 2.1.6 -- "open circuit generator voltage shall
not exceed 25 volts in magnitude".  "The generator [transmitter]
with a test load of 3000 to 7000 ohms [required receiver specs],
the potential at the interface point shall not be less than 5
volts nor more than 15 volts in magnitude".


> Since this transfer shall travel from 0.3 M - 200M i may need
> a potent voltage level and a good shielding.
>
> Which do you think is the best way too boost such a signal,

I wouldn't boost it.  I'd use a balanced transmission mechanism
like EIA-422.
                                               Lee Jones

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Jones Computer Communications             .....leeKILLspamspam@spam@frumble.claremont.edu
509 Black Hills Dr, Claremont, CA 91711         voice: 909-621-9008
-------------------------------------------------------------------

1999\05\15@213122 by Ian Cull

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In a message dated 99-05-15 14:56:44 EDT, you write:

> hi there i seem to recall that RS232 transmissions should be done over short
>  cables. since there are only -3/+3v levels, is this true.
>
>  Since this transfer shall travel from 0.3 M - 200M i may need a potent
>  voltage level and a good shielding.
>
The RS232 specification is, in many ways, vague ... and flexible.
In a previous job, we more than once ran RS232 links over 200M+ with no
trouble, at 9600baud.
If you have good voltage levels (+/-10V min) and good error
detection/correction, you can "abuse" the spec with little risk of problems
... keep the wires away from noisy equipment ... ensure good quality joins
... etc.

Ian C.

1999\05\16@010521 by Eric Oliver

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Perhaps you could switch to RS485 or convert from RS232 to RS485 then from
RS485 back to RS232 on the other end.  I think the MAX485 is the RS485
equivalent of the MAX232.  There's quite a bit of info on the Net regarding
RS485.

Eric

On Saturday, May 15, 1999 1:55 PM, Robert Mellgren
[SMTP:robert.mellgrenspamKILLspamVALHALLA.ORNSKOLDSVIK.COM] wrote:
> hi there i seem to recall that RS232 transmissions should be done over
short
> cables. since there are only -3/+3v levels, is this true.
>
> Since this transfer shall travel from 0.3 M - 200M i may need a potent
> voltage level and a good shielding.
>
> Which do you think is the best way too boost such a signal, should i
boost
> it straight from the output pin from the pic, with the help of a NPN
> transistor, that drains say.. 12v-24v then convert that level of voltage
> back to TTL with a 7805, is the 7805 fast enough? we are after all
talking
> 1200 baud here, i do not seem to find a datasheet that describes this.
>
> Or make some sort of optic transmission, ( which is less cheap ), via
optic
{Quote hidden}

1999\05\16@112632 by llgren

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o

1999\05\17@070853 by Caisson

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> Van: Robert Mellgren <.....robert.mellgrenKILLspamspam.....VALHALLA.ORNSKOLDSVIK.COM>> > Aan: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
> Onderwerp: Signal loss!?
> Datum: zaterdag 15 mei 1999 20:55

Hello Robert,

> hi there i seem to recall that RS232 transmissions should be done over
short
> cables. since there are only -3/+3v levels, is this true.

What you are describing is their _absolute minimum_ (output) voltage to be
considered RS232.  Its absolute maximum (output) voltage is (AFAIK) +16/-16
volt.  It's inputs are created to accept anything between +2/-2 to +16/-16
volts.  So Cranking-up the _output_ voltage to +12/-12 is no problem, and
can (should) be connected directly to another RS232 input.

Greetz,
 Rudy Wieser

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