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'[EE] Looking for single channel RS232 @2.5V'
2006\04\18@101945 by alan smith

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Not even looking at maxim....
 
 I am trying to find a single channel RS232 chip that runs on 2.5V.  I found a dual from TI (and oh happy day....TI is starting to cross to some Maxim parts) but would prefer the single for cost and footprint reasons.
 
 Any other favorites?

               
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2006\04\18@112105 by Alan B. Pearce

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>I am trying to find a single channel RS232 chip that
>runs on 2.5V. I found a dual from TI (and oh happy day
>....TI is starting to cross to some Maxim parts) but
>would prefer the single for cost and footprint reasons.

Looked at Intersil?

I received some samples of ISL81334 today, which is a two port RS232/485
chip, with each port individually configurable for the level standard. They
also make a single port version, and also check the J lead (I think) version
as it comes in a tinier package, but is a different part number.

They also do some other RS232 chips as well. Hmm just looked at
http://www.intersil.com/data/an/an9863.pdf which suggests a range of 3-5V
ones, not 2.5, but a number of the part numbers look like they would be
Maxim second source.

This one shows some 2.7V devices
http://www.intersil.com/products/deviceresults.asp?i=2500&i=10357

2006\04\18@140318 by alan smith

picon face
Thanks for the link....if they were not in QFN (those are just way hard to hand solder)

"Alan B. Pearce" <spam_OUTA.B.PearceTakeThisOuTspamrl.ac.uk> wrote:  >I am trying to find a single channel RS232 chip that
>runs on 2.5V. I found a dual from TI (and oh happy day
>....TI is starting to cross to some Maxim parts) but
>would prefer the single for cost and footprint reasons.

Looked at Intersil?

I received some samples of ISL81334 today, which is a two port RS232/485
chip, with each port individually configurable for the level standard. They
also make a single port version, and also check the J lead (I think) version
as it comes in a tinier package, but is a different part number.

They also do some other RS232 chips as well. Hmm just looked at
http://www.intersil.com/data/an/an9863.pdf which suggests a range of 3-5V
ones, not 2.5, but a number of the part numbers look like they would be
Maxim second source.

This one shows some 2.7V devices
www.intersil.com/products/deviceresults.asp?i=2500&i=10357

2006\04\18@214801 by Christian A. Weagle

flavicon
face
>   I am trying to find a single channel RS232 chip that runs on 2.5V.  

LTC makes a chip (not sure of the P/N), that I have used before, that can run down to at least 2.7V.  It uses an internal boost switcher (!) to generate the RS232 voltages.  The one I used was, ISTR, a quad, but they may have others in that series, now.

2006\04\19@193702 by Marc Nicholas

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Hi Alan,

Does it need to be "real" RS232? Or will what passes for RS232 on most PCs
do?

If the latter, I have a neat solution involving a SOT23 transistor array ;-)


-marc

On 4/18/06, alan smith <.....micro_eng2KILLspamspam@spam@yahoo.com> wrote:
{Quote hidden}

>

2006\04\20@160512 by alan smith

picon face
nope...has to be real RS232 levels.....interfacing with unknown devices, but they will assume 232 levels.
 
 Might post what you have tho, just as a point of reference for others.

Marc Nicholas <geekythingspamKILLspamgmail.com> wrote:
 Hi Alan,

Does it need to be "real" RS232? Or will what passes for RS232 on most PCs
do?

If the latter, I have a neat solution involving a SOT23 transistor array ;-)


-marc

On 4/18/06, alan smith wrote:
{Quote hidden}

>

2006\04\20@160549 by alan smith

picon face
nope...has to be real RS232 levels.....interfacing with unknown devices, but they will assume 232 levels.
 
 Might post what you have tho, just as a point of reference for others.

Marc Nicholas <.....geekythingKILLspamspam.....gmail.com> wrote:
 Hi Alan,

Does it need to be "real" RS232? Or will what passes for RS232 on most PCs
do?

If the latter, I have a neat solution involving a SOT23 transistor array ;-)


-marc

On 4/18/06, alan smith wrote:
{Quote hidden}

>

2006\04\21@022712 by Vasile Surducan

face picon face
On 4/20/06, alan smith <EraseMEmicro_eng2spam_OUTspamTakeThisOuTyahoo.com> wrote:
> nope...has to be real RS232 levels.....interfacing with unknown devices, but they will assume 232 levels.

Then forget it. There is no 2.5V part which is producing with charge
pump a *true* RS232 level. Even the 3V part (ie MAX3232) does not
produce a *true* RS232 level. Maybe you should define first which is
the RS232 true level ?

greetings,
Vasile



{Quote hidden}

> > --

2006\04\29@190136 by andrew kelley

picon face
On 4/21/06, Vasile Surducan <@spam@piclist9KILLspamspamgmail.com> wrote:
> On 4/20/06, alan smith <KILLspammicro_eng2KILLspamspamyahoo.com> wrote:
> > nope...has to be real RS232 levels.....interfacing with unknown devices, but they will assume 232 levels.
>
> Then forget it. There is no 2.5V part which is producing with charge
> pump a *true* RS232 level. Even the 3V part (ie MAX3232) does not
> produce a *true* RS232 level. Maybe you should define first which is
> the RS232 true level ?
>
> greetings,
> Vasile

No 2.5V part?  There should be since, rs232 levels are (from memory)
from +-3v to +-27v respsectively.  A voltage doubler would accomplish
+5v and a voltage doubler on the negative side could put out also a
-5v..  So I don't see why there isn't a 2.5v part, or at least one
that could be made using suitable voltage doubler chips.

andrew

2006\04\29@223458 by William Chops Westfield

face picon face

On Apr 29, 2006, at 4:01 PM, andrew kelley wrote:

> No 2.5V part?  There should be since, rs232 levels are (from memory)
> from +-3v to +-27v respsectively.  A voltage doubler would accomplish
> +5v and a voltage doubler on the negative side could put out also a
> -5v..  So I don't see why there isn't a 2.5v part...

Down at the low voltages, you have to start paying attention to
those "little" losses.  A voltage doubler circuit usually gives
you something like 2*(V - Vdiode)  If you start with 2.5V, you
probably only get out 3.6V, and then you lose Vcesat in the driver
part, and someone claimed it was supposed to be 3V guaranteed at
the other end of the wire which means 4+V at the driver output...

Don't most 2.5V circuits tend to have at least 3.3V somewhere for
IO drivers?  You won't see any 2.5V batteries, either...

Are there proposed standards for "long distance" serial communication
that will work well at the reduced voltage levels of modern systems?

BillW

2006\04\30@030818 by Wouter van Ooijen

face picon face
> No 2.5V part?  There should be since, rs232 levels are (from memory)
> from +-3v to +-27v respsectively.

IIRC it is +/- 5.0 minimum at the sender side, +/- 3.0 at the receiver.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2006\04\30@102603 by Gerhard Fiedler

picon face
William ChopsWestfield wrote:

> Are there proposed standards for "long distance" serial communication
> that will work well at the reduced voltage levels of modern systems?

RS-485/422 uses lower voltages than RS-232, and the most common physical
interface used with the CAN bus (ISO 11898-2) has still lower voltages. But
they are all above the 0...2.5V range.

There are probably economic limits... the circuitry required to compensate
for the lower physical S/N ratio is not cheap either, so just using a 5 V
ISO 11898-2 driver may be the cheaper solution.

Gerhard

2006\04\30@103333 by Vasile Surducan

face picon face
On 4/29/06, andrew kelley <RemoveMEleetslackerTakeThisOuTspamgmail.com> wrote:
> On 4/21/06, Vasile Surducan <spamBeGonepiclist9spamBeGonespamgmail.com> wrote:
> > On 4/20/06, alan smith <TakeThisOuTmicro_eng2EraseMEspamspam_OUTyahoo.com> wrote:
> > > nope...has to be real RS232 levels.....interfacing with unknown devices, but they will assume 232 levels.
> >
> > Then forget it. There is no 2.5V part which is producing with charge
> > pump a *true* RS232 level. Even the 3V part (ie MAX3232) does not
> > produce a *true* RS232 level. Maybe you should define first which is
> > the RS232 true level ?
> >
> > greetings,
> > Vasile
>
> No 2.5V part?  There should be since, rs232 levels are (from memory)
> from +-3v to +-27v respsectively.

+-3V on the receiver side. Use any MAX3232 or clone, supply it on 2.5V
and try to communicate over 500m of cable with a PC. If you can, I'll
buy you a beer, the best ameican one (yacksss...).

greetings,
Vasile


A voltage doubler would accomplish
> +5v and a voltage doubler on the negative side could put out also a
> -5v..  So I don't see why there isn't a 2.5v part, or at least one
> that could be made using suitable voltage doubler chips.
>
> andrew
>
> -

2006\04\30@122037 by alan smith

picon face
Hmmm...I've opened a can of worms on this one!  My spec was revised...I can run this at 3V now, and I don't need to talk over 500M, less than 1M typical to some "unknown/undefined" device, but just RS232.  I found that TI makes some Maxim clone parts, looking at those now.

Vasile Surducan <RemoveMEpiclist9spamTakeThisOuTgmail.com> wrote:  On 4/29/06, andrew kelley wrote:
> On 4/21/06, Vasile Surducan
wrote:
{Quote hidden}

+-3V on the receiver side. Use any MAX3232 or clone, supply it on 2.5V
and try to communicate over 500m of cable with a PC. If you can, I'll
buy you a beer, the best ameican one (yacksss...).

greetings,
Vasile


A voltage doubler would accomplish
> +5v and a voltage doubler on the negative side could put out also a
> -5v.. So I don't see why there isn't a 2.5v part, or at least one
> that could be made using suitable voltage doubler chips.
>
> andrew
>
> -

2006\04\30@152441 by William Chops Westfield

face picon face
On Apr 30, 2006, at 7:33 AM, Vasile Surducan wrote:

> try to communicate over 500m of cable with a PC.

rs232 isn't spec'ed for 500m of cable.  IIRC, it has specs like:
1) maximum speed 19200
2) 19200 has a cable length limit of about 20 feet.
3) "HW flow control" doesn't exist.
4) a rather complex set of modem signal exchanges is REQUIRED.

In short, rs232 is one of the widely and flagrantly violated
specifications in the history of electronics.  Go ahead and stick
a driver designed for 3.3V in your 2.5V circuit and see if it
works.   Measure it, see if you feel comfortable with the output.
If you're felling adventuresome, try it at various speeds
and cable lengths with various remote ends, and figure out what
the limits are, and then tell us...

Alternately, the market is full of inductor based voltage converters
that will boost 2.5V to 5V (or higher), thanks to the desire to
power 5V logic from batteries.  You might even save money using
something like Blick's 3T boost regulator to drive old-fashioned
multi-supply driver chips...

(cisco has an 16/32 port rs232 async card that uses 5V driver
chips (16 or 32+ of them.)  Groan.  I don't know what they were
thinking.  (of course, it does NOT exhibit the infamous "break
problem", so perhaps that's what they were thinking...))

BillW


'[EE] Looking for single channel RS232 @2.5V'
2006\05\02@080336 by Alan B. Pearce
face picon face
>rs232 isn't spec'ed for 500m of cable.  IIRC, it has specs like:
>1) maximum speed 19200
>2) 19200 has a cable length limit of about 20 feet.
>3) "HW flow control" doesn't exist.

I guess RTS control of a multidrop modem isn't flow control? CTS says the
link is ready to accept.

2006\05\02@081243 by Michael Rigby-Jones

picon face


>-----Original Message-----
>From: piclist-bouncesEraseMEspam.....mit.edu [EraseMEpiclist-bouncesspammit.edu]
>Sent: 02 May 2006 13:04
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] Looking for single channel RS232 @2.5V
>
>
>>rs232 isn't spec'ed for 500m of cable.  IIRC, it has specs like:
>>1) maximum speed 19200
>>2) 19200 has a cable length limit of about 20 feet.
>>3) "HW flow control" doesn't exist.
>
>I guess RTS control of a multidrop modem isn't flow control?
>CTS says the link is ready to accept.

RTS/CTS is generaly controlled by software rather than the UART though, so not HW flow control?

Regards

Mike

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2006\05\02@083520 by Alan B. Pearce

face picon face
>RTS/CTS is generaly controlled by software rather than
>the UART though, so not HW flow control?

Err, yes, but then the same goes for almost any flow control system.

2006\05\02@113911 by William Chops Westfield

face picon face

On May 2, 2006, at 5:03 AM, Alan B. Pearce wrote:

>> 3) "HW flow control" doesn't exist.
>
> I guess RTS control of a multidrop modem isn't flow control?
> CTS says the link is ready to accept.

Officially RTS/CTS are used for half-duplex line "turn around",
a somewhat flow-control-like function.

BillW

2006\05\02@173642 by Howard Winter

face
flavicon
picon face
Michael,

On Tue, 2 May 2006 13:12:40 +0100, Michael Rigby-Jones wrote:

{Quote hidden}

Errr - no!  It doesn't work like that.  It's nothing to do with where the decision is made, but how the
signals travel between sender and receiver.

HW flow control uses RTS/CTS signals on separate channels (wires) from the data (sometimes called "out of band
signalling").
SW flow control sends XON / XOFF characters in the normal data channels to start and stop the data flow ("in
band signalling").

Cheers,


Howard Winter
St.Albans, England


2006\05\02@210559 by Vasile Surducan

face picon face
On 4/30/06, alan smith <RemoveMEmicro_eng2TakeThisOuTspamspamyahoo.com> wrote:
{Quote hidden}

A doubler will works ok with small load. As long the cable will  be,
as high the parasitical capacitance. Adding the receiver load (which
could be less than 7K) and surprise, there will not be 5V as expected
but much less.
One example is the MAX232. Supplied at +5V you should get +/-10V right ?
You'll get +/-8V in the best circumstance with a standard load.
So the theory is one and the practice is else.


greetings,
vasile

> >
> > andrew
> >
> > --

2006\05\02@210730 by Vasile Surducan

face picon face
On 4/30/06, William Chops Westfield <RemoveMEwestfwKILLspamspammac.com> wrote:
> On Apr 30, 2006, at 7:33 AM, Vasile Surducan wrote:
>
> > try to communicate over 500m of cable with a PC.
>
> rs232 isn't spec'ed for 500m of cable.

are you sure ? which specs do you have ?

 IIRC, it has specs like:
{Quote hidden}

> -

2006\05\02@214303 by William Chops Westfield

face picon face
On May 2, 2006, at 6:07 PM, Vasile Surducan wrote:

>> rs232 isn't spec'ed for 500m of cable.
>
> are you sure ? which specs do you have ?
>
Well, for instance:
   http://www.lammertbies.nl/comm/info/RS-232_specs.html

Max speed 20kbps, max drive capacitance 2500pf (which is about
50m worth of CAT5...)  To go 500m, you'd supposedly have to run
somewhat below 4800bps.

I don't know if there's been any formalization of the modern
DB9, 115200bps, etc world...

http://en.wikipedia.org/wiki/RS-232C has some of the issues
highlighted...

BillW

2006\05\03@000914 by Dave Lag

picon face
Max speed 20kbps, max drive capacitance 2500pf (which is about
50m worth of CAT5...)  To go 500m, you'd supposedly have to run
somewhat below 4800bps.

BillW
--

I recall our techs would run a (couple?) hundred feet of what they
called "low cap" at 19200 around the c.o.
Didn't work with the regular specified cable but saved on line drivers.
D

2006\05\03@050132 by William Chops Westfield

face picon face

On May 2, 2006, at 9:09 PM, Dave Lag wrote:
>
>> Max speed 20kbps, max drive capacitance 2500pf (which is about
>> 50m worth of CAT5...)  To go 500m, you'd supposedly have to run
>> somewhat below 4800bps.
>
> I recall our techs would run a (couple?) hundred feet of what they
> called "low cap" at 19200 around the c.o.

Don't confuse "the spec" with "what works."  There's a REASON that
rs232 is the most widely violated specification in the world: in
most cases it still works.  The original spec must have assumed
lamp cord run through transmitter rooms and receivers made from
homemade vacuum tubes, or something (and we KNOW it assumed
half-duplex modems of incredible dumbness.)  When I worked at Stanford,
200+ feet at 9600bps was all over the place, and I don't remember
anyone ever moving a terminal server to get it closer to the
actual terminals...  That pre-dated "modern" rs232 drivers, so
you were talking (probably) 1488/1489s...

BillW

2006\05\05@011331 by William Chops Westfield

face picon face
> On Apr 29, 2006, at 4:01 PM, andrew kelley wrote:
>
>> No 2.5V part?

Guess what I saw in this week's EET?
Linear Technology now has several rs232 transceiver chips
that operate off 1.8 to 5.5V.  Looks like they use an inductor
switching regulator to get appropriate voltage, and then a
switch cap setup to get negative appropriate voltage.  Right
up your alley...  LTC2801 and similar.

http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1007,C1016,P10430

Free samples, but nasty packages :-(

BillW

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