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'[EE] microcontroller with built-in RS-485?'
2006\02\25@115652 by Jesse Lackey

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Hello all, I often have designs that need rs-485 with some relatively
simple microcontroller code, and it is always been a two-chip solution:
75176 (or equivalent with improvements) and a PIC of some sort.

Does anyone know of a microcontroller with a built-in RS-485
transceiver?  Ideally it would have a UART (pretty much a necessity, but
not absolutely required), 16 pins or less, and a decent C compiler
available from the vendor or 3rd party that doesn't cost a kilobuck.
Freeware versions limited to say 4K codespace are acceptable.

I haven't done an exhaustive search but I've never seen rs-485 built-in
to a micro, which is a bit surprising in a way.

Anyway, love to hear anyone's experiences.
Thanks-
Jesse

2006\02\25@123305 by Josh Koffman

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On 2/25/06, Jesse Lackey <spam_OUTjsl-mlTakeThisOuTspamcelestialaudio.com> wrote:
> I haven't done an exhaustive search but I've never seen rs-485 built-in
> to a micro, which is a bit surprising in a way.

Maybe I've never really looked, but are there any micros with built in RS232?

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

2006\02\25@140839 by Douglas Wood

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I've not ever seen a micro with RS-anything built into the micro itself. I
wouldn't want one, either. If the RS-485 (or RS-422/232/etc.) part of the
circuit got fried, you'd have to replace the entire micro, not just the much
less expensive transceiver chip.

{Original Message removed}

2006\02\25@143841 by Gökhan SEVER

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9-bit mode in ausart modul isnt enough for rs-485 systems?

an excerpt from the 18fxx2 datasheet

16.2.3 SETTING UP 9-BIT MODE WITH
ADDRESS DETECT
"This mode would typically be used in RS-485 systems."

2006\02\25@144313 by Rich Graziano

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Isn't the so-called EIA/RS 232 in the MCS51 series really an RS/422 because
it is only a 5 volt function and not the bipolar EIA/RS232 requirement?  I
think this is why the MAX232 or other external part is required.  Is the
only difference between RS/232 and RS/422 the level shifting?  Is the
protocol the same?
Rich
{Original Message removed}

2006\02\25@151444 by olin piclist

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Douglas Wood wrote:
> I've not ever seen a micro with RS-anything built into the micro
> itself. I wouldn't want one, either. If the RS-485 (or
> RS-422/232/etc.) part of the circuit got fried, you'd have to replace
> the entire micro, not just the much less expensive transceiver chip.

This seems to be a common position, but does it really matter?  In most
cases if the unit fries, you are going to replace the whole unit.  Whether
that's due to the RS-232 interface or the micro doesn't make any difference.
It just doesn't make sense to spend $50 technician time to diagnose and
repair the problem on a $40 board.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\02\25@154255 by Dwayne Reid

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At 09:56 AM 2/25/2006, Jesse Lackey wrote:
>Hello all, I often have designs that need rs-485 with some relatively
>simple microcontroller code, and it is always been a two-chip solution:
>75176 (or equivalent with improvements) and a PIC of some sort.
>
>Does anyone know of a microcontroller with a built-in RS-485
>transceiver?  Ideally it would have a UART (pretty much a necessity, but
>not absolutely required), 16 pins or less, and a decent C compiler
>available from the vendor or 3rd party that doesn't cost a kilobuck.
>Freeware versions limited to say 4K codespace are acceptable.

I've not ever seen a micro with built-in RS-232 or RS-422 or RS-485
drivers.  I suspect one of the reasons is the requirement to
withstand some serious electrical abuse.

Couple of points:

1) I always try to use a socketed DIP RS-xxx driver in my designs -
even those boards that are otherwise completely SMT.  I've spent far
too much time replacing blown interface chips on other people's
designs.  Friend of mine goes through the same thing whenever we get
serious thunderstorms near our local stadium - RS422 drivers and
receivers die in the Sony Jumbotron video screen.  Sadly - those are
so14.  Easy to change but the pads get tired after several dozen replacements.

2) If all you need is RS-422 or RS-485 transmit only (no receive),
bit-bang it.  I've done balanced data (2 complimentary outputs)
transmit at 250Kb/s (DMX) on a 4 MHz PIC.  IOW - 4 instructions per
bit with both output lines changing state at the same instant.  PIC
outputs are protected with a couple of P6KE7.5A tranzorbs.

dwayne

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2006\02\25@223335 by Neil Cherry

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Olin Lathrop wrote:
> Douglas Wood wrote:
>> I've not ever seen a micro with RS-anything built into the micro
>> itself. I wouldn't want one, either. If the RS-485 (or
>> RS-422/232/etc.) part of the circuit got fried, you'd have to replace
>> the entire micro, not just the much less expensive transceiver chip.
>
> This seems to be a common position, but does it really matter?  In most
> cases if the unit fries, you are going to replace the whole unit.  Whether
> that's due to the RS-232 interface or the micro doesn't make any difference.
> It just doesn't make sense to spend $50 technician time to diagnose and
> repair the problem on a $40 board.

Olin, I've seen fried transceiver chips on tons of equipment. I've
referred to them as self sacrificing (I think others have too). It
got to the point that when a particular board came in to be repaired
that I'd just replace the Moto MC1489 without any other testing. 95%
of the time the board would work. The $2 (US) part would save a $1500
board (this was back in the mid 80's). I still kind of design things
that way today (sacrificing parts separate from the main board). Of
course I just do it as a hobby now which is definitely a different
prospective from the board swap culture today.

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2006\02\27@110711 by William Killian

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> -----Original Message-----
> From: .....piclist-bouncesKILLspamspam.....mit.edu [EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu] On
Behalf
> Of Josh Koffman
> Sent: Saturday, February 25, 2006 12:33 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] microcontroller with built-in RS-485?
>
> On 2/25/06, Jesse Lackey <jsl-mlspamspam_OUTcelestialaudio.com> wrote:
> > I haven't done an exhaustive search but I've never seen rs-485
built-in
> > to a micro, which is a bit surprising in a way.
>
> Maybe I've never really looked, but are there any micros with built in
> RS232?
>
> Josh

I'm used to controllers having the serial interface built in but using a
separate driver chip.  The processor does about 0 or 5 VDC whith the
driver doing the +/- 5-12VDC.  Once you have the separate driver chip
the 232 vs. 485 is immaterial to the controller - it's the same to the
U[S]ART.



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2006\02\27@115116 by Josh Koffman

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On 2/27/06, William Killian <KILLspamwilliam.killianKILLspamspamvgt.net> wrote:
> I'm used to controllers having the serial interface built in but using a
> separate driver chip.  The processor does about 0 or 5 VDC whith the
> driver doing the +/- 5-12VDC.  Once you have the separate driver chip
> the 232 vs. 485 is immaterial to the controller - it's the same to the
> U[S]ART.

Me too - that was sort of my point. I've used the UART in the PICs for
both RS232 and RS485 with success. It gives me greater flexibility in
my micro choices, and I don't have to stock two different ones based
on the serial interface alone.

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

2006\02\27@122244 by David VanHorn

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While internal drivers could be done, it's a real mess for the uP vendor.
For most interfaces, you have to incorporate much more robust ESD protection
than is typically done in micros, and you have to deal with higher voltages.
232 for example, CAN be driven by as much as +/- 25V. Anything you put out
there for 232 had better be able to deal with that.

I agree it's a "would be nice if", but I don't expect to see it happen.

2006\02\27@145116 by Gerhard Fiedler

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David VanHorn wrote:

> I agree it's a "would be nice if", but I don't expect to see it happen.

Yes... just multiply the number of processors with UARTs with the number of
different classes of interface drivers that get hooked up to them, and you
know why :)

Gerhard

2006\02\27@192603 by Chen Xiao Fan

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> -----Original Message-----
> From: RemoveMEpiclist-bouncesTakeThisOuTspammit.edu
> [spamBeGonepiclist-bouncesspamBeGonespammit.edu] On Behalf Of Jesse Lackey
>
> I haven't done an exhaustive search but I've never seen
> rs-485 built-in to a micro, which is a bit surprising in
> a way.

If RS232 and RS485 were 5V or 3.3V bus, then the
transceivers would have been integrated.

If you look at USB PICs, they have USB transceivers integrated.
They can use external USB transceivers as well.

Regards,
Xiaofan

2006\02\27@203131 by Gerhard Fiedler

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Chen Xiao Fan wrote:

> If RS232 and RS485 were 5V or 3.3V bus, then the transceivers would have
> been integrated.

I don't think the voltage is the reason. The standard RS-232 drivers do run
off a 5V supply, despite the different line voltages required.


> If you look at USB PICs, they have USB transceivers integrated. They can
> use external USB transceivers as well.

The USB bus standard has a clear spec, down to the deepest levels of layer
1 (even the plugs are specified). That's why there are USB processors that
have the hardware interface integrated: because there is only one hardware
interface. They would have it integrated just as well if the bus ran with
12V.

For serial communication, there are many different standards, and many more
non-standard implementations that are so by their non-standard
requirements. IMO this multitude of hardware interfaces is the reason they
don't integrate it, not the voltage levels. (And, as others have already
said, the much higher exposure to spikes and other nasty noise for this
type of interface may also be a reason. USB won't be used over 200m of
factory floor :)

Gerhard

2006\02\28@013019 by Robert Ammerman

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There is a very simple reason that transceivers are not integrated on
microcontrollers: process limits

Each semiconductor process used to build microcontrollers has different
limits on characteristics like maximum voltages. Notice the new dsPIC33's
which don't even go to 5V!

Another example is the nearly useless Microchip LDO regulators with a Vin
max of 6V.

Bob Ammerman

{Original Message removed}

2006\02\28@015556 by Ruben Jönsson

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I am very surprised to see that there are som many RS485 circuits in real world
applications that doesn't use any protection on the transmission lines
whatsoever. Several hundreds of meters of wire directly in to a chip! It seems
to be accepted that these type of chips are expendable.

/Ruben


> (And, as others have already
> said, the much higher exposure to spikes and other nasty noise for this
> type of interface may also be a reason. USB won't be used over 200m of
> factory floor :)
>
==============================
Ruben Jönsson
AB Liros Electronic
Box 9124, 200 39 Malmö, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
TakeThisOuTrubenEraseMEspamspam_OUTpp.sbbs.se
==============================

2006\02\28@044323 by John Ward

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ok... here comes the field leveller.... you connect two buildings together
... both at varying ground potential...

An RS-485 driver has better chance of surviving a quick earth fault/spike
... than the core of your CPU ? which might behave erraticly.. etc etc



On 2/28/06, Ruben Jönsson <RemoveMErubenspamTakeThisOuTpp.sbbs.se> wrote:
{Quote hidden}

>

2006\02\28@061437 by Alan B. Pearce

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>Does anyone know of a microcontroller with
>a built-in RS-485 transceiver?

No, but for those interested, Intersil have recently introduced some single
and dual port RS232/RS422/RS485 transceivers. The dual ones can have either
port configured as RS232 or RS422/485. If you get the tiny 40 pin package
you can control the RS422/485 slew rate to one of three rates - separately
for each port if both ports are RS422/485.

Look for ISL81334/81337/41334/41337 on the Intersil web site.

2006\02\28@061620 by Alan B. Pearce

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>Maybe I've never really looked, but are there
>any micros with built in RS232?

Some think that there are PICs like this - they only need a series
protection resistor ;)))))))))))

2006\02\28@070643 by olin piclist

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Gerhard Fiedler wrote:
> They would have it integrated just as well if the bus ran with 12V.

I don't think so.  The upper voltage is usually a process limitation.  I
wouldn't be easy to add 12V I/O to a microcontroller optimized to operate at
5V.  Look at the Microchip line of analog parts like most of their opamps
and voltage regulators.  These have great specs until you notice that they
only work up to 6V supply.  I've asked about this because it greatly reduces
the possible applications for their chips and was told it was due to a
limitation of the process for making 5V microcontrollers.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\02\28@074652 by olin piclist

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John Ward wrote:
> ok... here comes the field leveller.... you connect two buildings
> together ... both at varying ground potential...
>
> An RS-485 driver has better chance of surviving a quick earth
> fault/spike ... than the core of your CPU ? which might behave
> erraticly.. etc etc

When lightning raises the ground potential of one building by 10KV with
respect to the other, it won't matter if your micrcocontrollers were
connecte via RS-232, RS-485, or native 5V UART.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\02\28@095536 by Gerhard Fiedler

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Olin Lathrop wrote:

> When lightning raises the ground potential of one building by 10KV with
> respect to the other, it won't matter if your micrcocontrollers were
> connecte via RS-232, RS-485, or native 5V UART.

Are there any statistics how often this happens? Something like probability
vs ground potential difference?

Gerhard

2006\02\28@101918 by olin piclist

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Gerhard Fiedler wrote:
> Are there any statistics how often this happens? Something like
> probability vs ground potential difference?

There is a net of radio receivers around the world that measure the location
of lightning strikes.  This database has been used to determine the relative
probability of lighting strikes in different geographic regions.  I sortof
remember a hot spot around central around Orlando, for example.

Ground potential difference has a lot to do with the exact location of a
lighting strike.  A few meters can make a big difference.  The current paths
are also not obvious, so 50 meters away in one case may be as bad as 10
meters in another case.

I therefore don't think the statistics would be relevant to a design anyway,
since it would need to handle the worst case well enough so that nobody gets
hurt, or at least nobody gets sued.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\02\28@113533 by David VanHorn

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I had an amusing incident with a 485 system in a casino once.
The dir of engineering was insistent on using sheilded cable, and that both
ends of the cable be tied to ground.

Unfortunately, "ground" isn't always ground, and tying both ends of the
shield is a really bad idea, especially when there's about 6VAC differential
between "Grounds" and a lot of amps available.

We got the cables disconnected before anything got too far out of hand :)

2006\02\28@133515 by Ruben Jönsson

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> I had an amusing incident with a 485 system in a casino once.
> The dir of engineering was insistent on using sheilded cable, and that both
> ends of the cable be tied to ground.

Using a shielded cable, both ends should be tied to the chassis of the
equipment (which should be ground and may or may not be 0V) - which is the
return path for the disturbing currents.

A shielded cable connected at only one end is virtualy useless as a shield for
conducted RF at the unconnected end (IEC/EN 61000-4-6).

> Unfortunately, "ground" isn't always ground, and tying both ends of the
> shield is a really bad idea, especially when there's about 6VAC differential
> between "Grounds" and a lot of amps available.

In that case the shield should be DC blocked with a capacitor, but still
connected.

What if both equipments had 0V connected to ground internally?

>
> We got the cables disconnected before anything got too far out of hand :)

==============================
Ruben Jönsson
AB Liros Electronic
Box 9124, 200 39 Malmö, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
EraseMErubenspampp.sbbs.se
==============================

2006\02\28@135133 by David VanHorn

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>
>
> A shielded cable connected at only one end is virtualy useless as a shield
> for
> conducted RF at the unconnected end (IEC/EN 61000-4-6).


Right, but there's other ways to solve that, and if the whole thing does a
meltdown due to ground differentials, it dosen't matter how good your
shielding was.


> In that case the shield should be DC blocked with a capacitor, but still
> connected.


I agree, but the DofE didn't see it that way.

What if both equipments had 0V connected to ground internally?


They did.

>
> > We got the cables disconnected before anything got too far out of hand
> :)


Smoke, but not fire.

2006\02\28@161450 by Ruben Jönsson

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I just found a rather good article about the subject (shielding, that is) that
I thought would be worth sharing.

<www.cherryclough.com/Downloads/The%20benefits%20of%20applying%2061000-5-
2%20to%20cable%20shield%20bonding%20and%20earthing,%2021%20May%2004.doc>

/Ruben

{Quote hidden}

> -

2006\02\28@185311 by Peter

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On Tue, 28 Feb 2006, Gerhard Fiedler wrote:

> Olin Lathrop wrote:
>
>> When lightning raises the ground potential of one building by 10KV with
>> respect to the other, it won't matter if your micrcocontrollers were
>> connecte via RS-232, RS-485, or native 5V UART.
>
> Are there any statistics how often this happens? Something like probability
> vs ground potential difference?

You mean, probability vs:

(day_of_week == Sun) * 100  +
(cost_of_installation >= $10k) * 10,000 +
(not_insured == true) * 100,000 +
(not_paid_for_yet == tru) * 1,000,000

Murphy never sleeps. If you want to know what lightning is up to you can
read some very interesting reports at the American Lightning Instiute:

http://www.lightningsafety.com/

An insurance company will likly have the best data on this kind of
problem (together with the local phone company ... hehehe)

Peter

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