Re: [Emc-users] Modbus RS-485 Transceiver

[Erik Christiansen]

On Mon, Feb 04, 2008 at 08:25:31PM -0800, Kirk Wallace wrote:
> 
> So the ground, will only be usable if all the transceivers are isolated,
> so that the ground wire is actually a 0V network common?

As I understand it, the pinouts.ru circuit runs network ground and power
to each node, making it a 4-wire bus. The node (e.g. PC or controller
card) ground is isolated. (Two occurrences of different earth symbol on
LHS of the diagram.) I'd use that method between machines. (Though I
hadn't planned that far, until this discussion. ;-) It'll be necessary
to source good optocouplers though, if high baudrates are planned.

Common power ground should be OK, on the machine, without isolated
transceivers, I expect, because it makes everything relatively
equipotential, certainly within the common-mode tolerance of the
receivers. The recommended 100 ohm resistors are "defeated" by being
shorted out by a common ground, but that's OK. If one part of the
machine runs off a separate plug pack (wall wart?), the 100 ohms will
pull the network ground into line.

> 
> I was given a link to RS485.com and found that they present schematics
> for all the products I looked at. I found it very educational too.

I'll have to have a look at that.

> I didn't really want to build an adapter, but the adapters I had seen up
> until recently were too expensive. I have been given links to some
> inexpensive adapters, but now I am learning they may have deficiencies.
> Now the question is, do I go with what may work well enough (especially
> over the length of a CNC machine) or what is more technically correct.
> Some of the literature I have read seems to indicate that in the real
> RS485 world that it may be more practical to set the network up and then
> tune the termination, bias and etc. as needed. This RS485 thing seems to
> be a project in itself.

Well put. I don't have practical experience using RS485 in noisy
environments, so I'm also collecting field know-how to supplement my
theoretical training.

It is my intention to run cat5 cable around my machine, inside some
plastic sheathed (oil-resistant) flexible steel conduit I bought on
sale. The metal conduit, and the twisted pairs of the cat5, will reduce
EMI susceptibility. (And the twisted pair should have a characteristic
impedance close to 120 ohm, so there should be little need to tweak the
termination.)

To go off the machine, over unscreened cat5, I have to consider
opto-isolation, as used in the pinouts.ru design, and a bus power supply
to preserve the separation of the two grounds. Fortunately, I've only
just started the design of the board which handles off-machine comms.

> Thanks for the help Erik.

No worries. :-)
I'm hacking my way through the same jungle. Your clarity of thought has
helped me stop to take a most timely look at the compass.

Erik


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Re: [Emc-users] Modbus RS-485 Transceiver

[Kirk Wallace]

On Mon, 2008-02-04 at 21:22 -0600, Javid Butler wrote:
> Kirk-
> 
> I have a very similar board with EIA-485 for the 40-pin PIC. It does have 
> complete control over the transciever.

That's good to know.

> What do you want to achieve with MODBUS and how soon do you want it done? 

I was hoping to make Modbus a part of EMC, but as a way point, make a
Modbus link to my VFD and ModIO (digital, analog, quadrature IO, Homann
Designs). My time table should be fairly long since I really should be
mounting encoders to my Bridgeport, but it's kind of cold out in the
shop these days.

> If 
> there is some code I'd be willing to work on porting it to the PIC, but I'm 
> loaded with projects right now so it will take a little time.

(If it's convenient, let us know what you are up to. Do you have a
website?)

>  It seems there 
> is an EMC MODBUS project forming, so maybe by the time the EMC code is 
> stable I'll have more time, or someone who knows the PIC will have time to 
> do the port.

There has been some discussion that for two (three?) wire Modbus, it may
not be possible to use a standard PC serial port due to a lack in
transceiver direction control. I saw that RS485.com had RS232 to RS485
adapters based on PIC's, but they are expensive, so I started wondering
about alternatives or if I could build one myself. At twenty to
thirty-five dollars each for a PIC board with an RS485 transceiver built
in, building is not necessary, but programming is. Now I'm trying to get
an idea of how hard it would be to do. I suppose, I could use a PIC that
is compatible with C and the libmodbus
( https://launchpad.net/libmodbus/ )
files as a model. I have an Olimex PIC-PG3 programmer and PIC-P14 (14
pin PIC) board. I may have to dust it off and play with it.

> Anyway, let me know if a board would be helpful. I've got several assembled. 
> I've also got a board based around the 17C44 with EIA-485 as well, but none 
> assembled.
> 
> Javid

Thanks for the help, Javid

-- 
Kirk Wallace (California, USA
http://www.wallacecompany.com/machine_shop/ 
Hardinge HNC lathe,
Bridgeport mill conversion, doing XY now,
Zubal lathe conversion pending)


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Re: [Emc-users] Modbus RS-485 Transceiver

[Kirk Wallace]

On Tue, 2008-02-05 at 14:37 +1100, Erik Christiansen wrote:
> On Sat, Feb 02, 2008 at 08:26:31PM -0800, Kirk Wallace wrote:
> > http://pinouts.ru/SerialPortsCables/rs485_cable_pinout.shtml
> > 
> > I plan on building a couple for my SJ200 application, and if you want I
> > can make an extra and send it over. I'm not sure when I'll have time to
> > build and test it -- probably in the next couple of weeks. Let me know.
> 
> Hi Kirk,
> 
> Though it looks like you're onto alternatives by now, it may be worth
> noting that there's no separate network ground wire in that design. From
> http://www.embeddedsys.com/subpages/resources/images/documents/microsys_art_RS485.pdf
> , I'm planning to follow:
> 
> "The RS-485 specification recommends connecting a 100 ohm resistor of at
> least 0.5 W in series between each node's signal ground and the
> network's ground wire, as Figure 1 shows. This way, if the ground
> potentials of two nodes vary, the resistors limit the current in the
> ground wire."
> 
> Admittedly, that's defeated if local ground goes back through the power
> supply, to mains earth.

So the ground, will only be usable if all the transceivers are isolated,
so that the ground wire is actually a 0V network common?

> Incidentally, the R9 + R12 bus bias chain is in parallel with the 120
> ohm R13, for bus termination purposes, giving under 86 ohms. (R13 = 200
> ohm would give a 120 ohm result) They're certainly biasing the bus
> heavily, which is good for noisy environments. (Thanks for the link.
> It's educational to see what others do.)
> 
> Erik

I was given a link to RS485.com and found that they present schematics
for all the products I looked at. I found it very educational too.

I didn't really want to build an adapter, but the adapters I had seen up
until recently were too expensive. I have been given links to some
inexpensive adapters, but now I am learning they may have deficiencies.
Now the question is, do I go with what may work well enough (especially
over the length of a CNC machine) or what is more technically correct.
Some of the literature I have read seems to indicate that in the real
RS485 world that it may be more practical to set the network up and then
tune the termination, bias and etc. as needed. This RS485 thing seems to
be a project in itself.

Thanks for the help Erik.

-- 
Kirk Wallace (California, USA
http://www.wallacecompany.com/machine_shop/ 
Hardinge HNC lathe,
Bridgeport mill conversion, doing XY now,
Zubal lathe conversion pending)


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Re: [Emc-users] Modbus RS-485 Transceiver

[Erik Christiansen]

On Sat, Feb 02, 2008 at 08:26:31PM -0800, Kirk Wallace wrote:
> http://pinouts.ru/SerialPortsCables/rs485_cable_pinout.shtml
> 
> I plan on building a couple for my SJ200 application, and if you want I
> can make an extra and send it over. I'm not sure when I'll have time to
> build and test it -- probably in the next couple of weeks. Let me know.

Hi Kirk,

Though it looks like you're onto alternatives by now, it may be worth
noting that there's no separate network ground wire in that design. From
http://www.embeddedsys.com/subpages/resources/images/documents/microsys_art_RS485.pdf
, I'm planning to follow:

"The RS-485 specification recommends connecting a 100 ohm resistor of at
least 0.5 W in series between each node's signal ground and the
network's ground wire, as Figure 1 shows. This way, if the ground
potentials of two nodes vary, the resistors limit the current in the
ground wire."

Admittedly, that's defeated if local ground goes back through the power
supply, to mains earth.

Incidentally, the R9 + R12 bus bias chain is in parallel with the 120
ohm R13, for bus termination purposes, giving under 86 ohms. (R13 = 200
ohm would give a 120 ohm result) They're certainly biasing the bus
heavily, which is good for noisy environments. (Thanks for the link.
It's educational to see what others do.)

Erik



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Re: [Emc-users] Modbus RS-485 Transceiver

[Javid Butler]

Kirk-

I have a very similar board with EIA-485 for the 40-pin PIC. It does have 
complete control over the transciever.

What do you want to achieve with MODBUS and how soon do you want it done? If 
there is some code I'd be willing to work on porting it to the PIC, but I'm 
loaded with projects right now so it will take a little time. It seems there 
is an EMC MODBUS project forming, so maybe by the time the EMC code is 
stable I'll have more time, or someone who knows the PIC will have time to 
do the port.

Anyway, let me know if a board would be helpful. I've got several assembled. 
I've also got a board based around the 17C44 with EIA-485 as well, but none 
assembled.

Javid



- Original Message - 
From: "Kirk Wallace" <[EMAIL PROTECTED]>
To: "Enhanced Machine Controller (EMC)" 
Sent: Monday, February 04, 2008 7:27 PM
Subject: Re: [Emc-users] Modbus RS-485 Transceiver


> This looks interesting. With this you could have complete control of the
> transceiver and timing. Too bad there is no software.
>
> http://microcontrollershop.com/product_info.php?products_id=651
>
> -- 
> Kirk Wallace (California, USA
> http://www.wallacecompany.com/machine_shop/
> Hardinge HNC lathe,
> Bridgeport mill conversion, doing XY now,
> Zubal lathe conversion pending)
>
>
> -
> This SF.net email is sponsored by: Microsoft
> Defy all challenges. Microsoft(R) Visual Studio 2008.
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> https://lists.sourceforge.net/lists/listinfo/emc-users
> 



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Re: [Emc-users] Modbus RS-485 Transceiver

[Kirk Wallace]

This looks interesting. With this you could have complete control of the
transceiver and timing. Too bad there is no software.

http://microcontrollershop.com/product_info.php?products_id=651

-- 
Kirk Wallace (California, USA
http://www.wallacecompany.com/machine_shop/ 
Hardinge HNC lathe,
Bridgeport mill conversion, doing XY now,
Zubal lathe conversion pending)


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Re: [Emc-users] Modbus RS-485 Transceiver offer/ a modbus library

[Geert De Pecker]

Chris,

For your info.
I downloaded the archive and it seemd to compile without problem (on my
laptop with opensuse 10.3):

1004tar xzf libmodbus-1.2.2.tar.gz
1005cd libmodbus-1.2.2
1006./configure
1007make

Geert

Chris Morley wrote:
> Kirk 
> I thank you for the offer for the r485 converter. I think after reading some 
> of the posts I would rather go with full duplex. Paying you for,  and 
> shipping, it would have been a pain too I think, as I am in Canada.
> I came across a web site with a Modbus library that is GPL.
> http://copyleft.free.fr/wordpress/index.php/libmodbus/
> In his trunk version he is working on a slave protocol - if I could get this 
> working I could set up two computers with rs 232 and test. prob test 
> classicladder too.
> The big but is that I cannot figure out how to auto make the program . I 
> downloaded automake and autoconfig but it doesn't work and I don't know how 
> to trouble shoot  the process. Any help would be great from anyone.
> Just thought it might be interesting to peruse or even use for your work.
> Thanks again.
> 
> Chris Morley
> 
> 
>> From: [EMAIL PROTECTED]
>> To: emc-users@lists.sourceforge.net
>> Date: Sat, 2 Feb 2008 20:26:31 -0800
>> Subject: [Emc-users] Modbus RS-485 Transceiver
>>
>> Chris Morley, 
>>
>> I have been pretty slow with work on Modbus. I just read your wiki post
>> and you indicated that you needed an RS-485 adapter. I found one here:
>>
>> http://pinouts.ru/SerialPortsCables/rs485_cable_pinout.shtml
>>
>> I plan on building a couple for my SJ200 application, and if you want I
>> can make an extra and send it over. I'm not sure when I'll have time to
>> build and test it -- probably in the next couple of weeks. Let me know.
>>
>> -- 
>> Kirk Wallace (California, USA
>> http://www.wallacecompany.com/machine_shop/ 
>> Hardinge HNC lathe,
>> Bridgeport mill conversion, doing XY now,
>> Zubal lathe conversion pending)
>>
>>
>> -
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>> Defy all challenges. Microsoft(R) Visual Studio 2008.
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> _
> 
> 
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Re: [Emc-users] Modbus RS-485 Transceiver offer/ a modbus library

[Kirk Wallace]

On Mon, 2008-02-04 at 09:36 -0500, Stephen Wille Padnos wrote:
... snip
> That's the library I used to make the HAL/Modbus component I needed.  
> I'll see if I can find out what I had to do to build it.  It works quite 
> well.
> 
> There is an annoying thing that library does - it prints error messages 
> without being asked.  If your slave device isn't attached, you'll get an 
> endless stream of "ERROR!  Communications timed out" messages on the 
> terminal.
> 
> Otherwise, it was pretty easy to get working.  I still haven't had a 
> chance to clean up my code for release, hopefully I'll get to that soon.
> 
> - Steve

That's good news Steve.

Anyone, please correct me if I am wrong, but it seems at least three of
us have been working in parallel to achieve the same thing, which is
integrate Modbus into EMC2. I would think that it would be more
efficient for us to parse the work and work together. On the other hand
it may be that this project is trivial enough to not warrant the fuss. 

Some thoughts do come to mind:

When I work as part of a project, my documentation and attention to
detail gets better. 

I have had to dust off my programming skills in order to achieve the
goals I have completed so far, which is a good thing, but it would be
nice to contribute in ways that am more proficient.

It would be nice to work on our organizational skills to get ready for a
bigger project like an open source CAD/CAM system.

It would be nice to be part of a group and not get stressed out about
anything. I get enough of that elsewhere.

Any thoughts on my thoughts?

-- 
Kirk Wallace (California, USA
http://www.wallacecompany.com/machine_shop/ 
Hardinge HNC lathe,
Bridgeport mill conversion, doing XY now,
Zubal lathe conversion pending)


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Re: [Emc-users] Modbus RS-485 Transceiver

[Stephen Wille Padnos]

Peter C. Wallace wrote:

>[snip]
>
>As someone else posted, full duplex links avoid the timing problem altogether.
>  
>
Actually, they don't eliminate all timing problems completely.  The 
slave devices still share a single set of wires, so a misconfigured 
slave can cause some havoc.  With a single slave device, there wouldn't 
be any turnaround problems though.

Anyone looking for hardware - check out .  They 
have loads of converters, repeaters, isolators, and other doodads for 
RS485.  Their stuff isn't the cheapest on the planet, but I've used 
various products of theirs for systems with up to 350 or so slaves, 
inside or outside, fixed or portable, etc.

- Steve


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Re: [Emc-users] Modbus RS-485 Transceiver offer/ a modbus library

[Stephen Wille Padnos]

Chris Morley wrote:

>Kirk 
>I thank you for the offer for the r485 converter. I think after reading some 
>of the posts I would rather go with full duplex. Paying you for,  and 
>shipping, it would have been a pain too I think, as I am in Canada.
>I came across a web site with a Modbus library that is GPL.
>http://copyleft.free.fr/wordpress/index.php/libmodbus/
>In his trunk version he is working on a slave protocol - if I could get this 
>working I could set up two computers with rs 232 and test. prob test 
>classicladder too.
>The big but is that I cannot figure out how to auto make the program . I 
>downloaded automake and autoconfig but it doesn't work and I don't know how to 
>trouble shoot  the process. Any help would be great from anyone.
>Just thought it might be interesting to peruse or even use for your work.
>Thanks again.
>  
>
That's the library I used to make the HAL/Modbus component I needed.  
I'll see if I can find out what I had to do to build it.  It works quite 
well.

There is an annoying thing that library does - it prints error messages 
without being asked.  If your slave device isn't attached, you'll get an 
endless stream of "ERROR!  Communications timed out" messages on the 
terminal.

Otherwise, it was pretty easy to get working.  I still haven't had a 
chance to clean up my code for release, hopefully I'll get to that soon.

- Steve


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Re: [Emc-users] Modbus RS-485 Transceiver

[[EMAIL PROTECTED]]

Sure this is also correct, but if you run realtime equipment through
485 it is not worth it to run unisolated interfaces.
It takes one voltage glitch or an inductive discharge close by or a
lightning strike far away or a charge buildup on the guard to induce
current in ground loops which are present in  non-isolated  converters.
It is not worth your workpiece missing a critical command in realtime.

If you use it for terminal programs like networking etc with error
correction, fine then it is not an issue, but for real-time, I will
never do that. Just one glitch and the workpiece is destroyed.

My company was one of the first to use RS485 in specific industries
back in 1988 with massive multi drop systems. We built a lot and learnt
a lot and see folks making the same mistakes we encountered and
resolved  almost 20 years back.

You have a ground loop, it is just a matter of time.


Javid Butler wrote:

  
  
  
  Isolation is commonly used to deal
with large common mode differentials. While that can blow a 485
tranciever it does not happen alot unless there are vey long cable runs
or the cable runs between buildings. When running 485 for distances of
a few hundred feet connecting equipment powered off the same mains
transformer it's unlikely that enough differential will occur, but a
quick check with a voltmeter before connecting equipment is always a
good idea.
   
  So both comments are correct. In
many cases 485 will run just fine without isolators, but some
applications definitely require isolation. I build 485 isolators, but
they are rarely tested to their limits. Often the isolation is more of
an insurance policy-it ensures that a single device cannot take down an
entire network segment.
   
  Javid
   
  
-
Original Message - 
From:
Dean Hedin 
To:
Enhanced Machine
Controller (EMC) 
Sent:
Sunday, February 03, 2008 9:15 PM
Subject:
Re: [Emc-users] Modbus RS-485 Transceiver


At 6 bucks a pop, buy 2.
 
Seriously,  I worked with 485 at a
previous job and I never blew out a non isolated converter.
Of course it might depend on what
your doing I guess.
 

  -
Original Message - 
  From:
  [EMAIL PROTECTED] 
  To:
  Enhanced Machine
Controller (EMC) 
  Sent:
Sunday, February 03, 2008 8:42 PM
  Subject:
Re: [Emc-users] Modbus RS-485 Transceiver
  
  
Good advice is never to buy non-isolated converters.
You will replace them regularly if you do.
This does not seem to be isolated.
  
  
Kirk Wallace wrote:
  
On Sun, 2008-02-03 at 03:06 -0500, Dean Hedin wrote:
  

  Interesting if you have the time..

But for six bucks and free shipping...
http://www.dealextreme.com/details.dx/sku.6040



Obviously, I didn't look hard enough when went looking for these. Thanks
for the link Dean.

  
  
  
   
  
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Re: [Emc-users] Modbus RS-485 Transceiver

[Javid Butler]

Isolation is commonly used to deal with large common mode differentials. While 
that can blow a 485 tranciever it does not happen alot unless there are vey 
long cable runs or the cable runs between buildings. When running 485 for 
distances of a few hundred feet connecting equipment powered off the same mains 
transformer it's unlikely that enough differential will occur, but a quick 
check with a voltmeter before connecting equipment is always a good idea.

So both comments are correct. In many cases 485 will run just fine without 
isolators, but some applications definitely require isolation. I build 485 
isolators, but they are rarely tested to their limits. Often the isolation is 
more of an insurance policy-it ensures that a single device cannot take down an 
entire network segment.

Javid
 
  - Original Message - 
  From: Dean Hedin 
  To: Enhanced Machine Controller (EMC) 
  Sent: Sunday, February 03, 2008 9:15 PM
  Subject: Re: [Emc-users] Modbus RS-485 Transceiver


  At 6 bucks a pop, buy 2.

  Seriously,  I worked with 485 at a previous job and I never blew out a non 
isolated converter.
  Of course it might depend on what your doing I guess.

- Original Message - 
From: [EMAIL PROTECTED] 
To: Enhanced Machine Controller (EMC) 
Sent: Sunday, February 03, 2008 8:42 PM
Subject: Re: [Emc-users] Modbus RS-485 Transceiver


Good advice is never to buy non-isolated converters.
You will replace them regularly if you do.
This does not seem to be isolated.


Kirk Wallace wrote: 
On Sun, 2008-02-03 at 03:06 -0500, Dean Hedin wrote:
  Interesting if you have the time..

But for six bucks and free shipping...
http://www.dealextreme.com/details.dx/sku.6040

Obviously, I didn't look hard enough when went looking for these. Thanks
for the link Dean.

  






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Re: [Emc-users] Modbus RS-485 Transceiver

[Dean Hedin]

At 6 bucks a pop, buy 2.

Seriously,  I worked with 485 at a previous job and I never blew out a non 
isolated converter.
Of course it might depend on what your doing I guess.

  - Original Message - 
  From: [EMAIL PROTECTED] 
  To: Enhanced Machine Controller (EMC) 
  Sent: Sunday, February 03, 2008 8:42 PM
  Subject: Re: [Emc-users] Modbus RS-485 Transceiver


  Good advice is never to buy non-isolated converters.
  You will replace them regularly if you do.
  This does not seem to be isolated.


  Kirk Wallace wrote: 
On Sun, 2008-02-03 at 03:06 -0500, Dean Hedin wrote:
  Interesting if you have the time..

But for six bucks and free shipping...
http://www.dealextreme.com/details.dx/sku.6040

Obviously, I didn't look hard enough when went looking for these. Thanks
for the link Dean.

  



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Re: [Emc-users] Modbus RS-485 Transceiver

[[EMAIL PROTECTED]]

Good advice is never to buy non-isolated converters.
You will replace them regularly if you do.
This does not seem to be isolated.


Kirk Wallace wrote:

  On Sun, 2008-02-03 at 03:06 -0500, Dean Hedin wrote:
  
  
Interesting if you have the time..

But for six bucks and free shipping...
http://www.dealextreme.com/details.dx/sku.6040

  
  
Obviously, I didn't look hard enough when went looking for these. Thanks
for the link Dean.

  





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[Emc-users] Modbus RS-485 Transceiver offer/ a modbus library

[Chris Morley]

Kirk 
I thank you for the offer for the r485 converter. I think after reading some of 
the posts I would rather go with full duplex. Paying you for,  and shipping, it 
would have been a pain too I think, as I am in Canada.
I came across a web site with a Modbus library that is GPL.
http://copyleft.free.fr/wordpress/index.php/libmodbus/
In his trunk version he is working on a slave protocol - if I could get this 
working I could set up two computers with rs 232 and test. prob test 
classicladder too.
The big but is that I cannot figure out how to auto make the program . I 
downloaded automake and autoconfig but it doesn't work and I don't know how to 
trouble shoot  the process. Any help would be great from anyone.
Just thought it might be interesting to peruse or even use for your work.
Thanks again.

Chris Morley


> From: [EMAIL PROTECTED]
> To: emc-users@lists.sourceforge.net
> Date: Sat, 2 Feb 2008 20:26:31 -0800
> Subject: [Emc-users] Modbus RS-485 Transceiver
> 
> Chris Morley, 
> 
> I have been pretty slow with work on Modbus. I just read your wiki post
> and you indicated that you needed an RS-485 adapter. I found one here:
> 
> http://pinouts.ru/SerialPortsCables/rs485_cable_pinout.shtml
> 
> I plan on building a couple for my SJ200 application, and if you want I
> can make an extra and send it over. I'm not sure when I'll have time to
> build and test it -- probably in the next couple of weeks. Let me know.
> 
> -- 
> Kirk Wallace (California, USA
> http://www.wallacecompany.com/machine_shop/ 
> Hardinge HNC lathe,
> Bridgeport mill conversion, doing XY now,
> Zubal lathe conversion pending)
> 
> 
> -
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> Defy all challenges. Microsoft(R) Visual Studio 2008.
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Re: [Emc-users] Modbus RS-485 Transceiver

[Javid Butler]

I thought about suggesting full duplex as well, but it involves converting 
every node of the network. For one or two nodes it's not bad, but it adds up 
quickly. It's not a hard conversion, but would still take time to do more 
than a couple of nodes.

Javid


- Original Message - 
From: "Peter C. Wallace" <[EMAIL PROTECTED]>
To: "Enhanced Machine Controller (EMC)" 
Sent: Sunday, February 03, 2008 10:07 AM
Subject: Re: [Emc-users] Modbus RS-485 Transceiver


> On Sun, 3 Feb 2008, Javid Butler wrote:
>
>> Date: Sun, 3 Feb 2008 08:27:42 -0600
>> From: Javid Butler <[EMAIL PROTECTED]>
>> Reply-To: "Enhanced Machine Controller (EMC)"
>>     
>> To: "Enhanced Machine Controller (EMC)" 
>> Subject: Re: [Emc-users] Modbus RS-485 Transceiver
>>
>> Kirk-
>>
>> With half duplex EIA-485 timing is very important. Unlike Ethernet, 
>> EIA-485
>> does not support collision detection at the physical layer so collisions
>> between outgoing data and returning data cause data corruption, since the
>> trancievers do not back off and retransmit. After a query the controller 
>> has
>> to release the line and allow the responder to talk.
>>
>> You will probably have to watch flow control. For what you want to do the
>> controller should transmit a query and then immediately tri-state, but
>> converting from EIA-232 it may hold the line high or low, perhaps
>> anticipating the next transmission. You might have to work with the way
>> messages are buffered-perhaps you will only be able to buffer one message 
>> at
>> a time.
>>
>> Javid
>
>
>
> Even without buffering you still need to wait until the character has been
> shifted out of the UARTs transmit shift register before line-turnaround. 
> You
> can do this by polling TBE and TSRE but you would have to poll fast enough 
> to
> meet the minimum response time of the Modbus peripheral. A better way is 
> to
> use a more advanced serial chip (Exar,OxfordSemi,NetMos) that includes 
> RS-485
> support. There are also some RS-232/RS-485 adapters that use a one-shot to
> enable the RS-485 Xmit enable, a little Mickey-Mouse but maybe ok at low 
> baud
> rates.
>
> As someone else posted, full duplex links avoid the timing problem 
> altogether.
>
>  > >
>> - Original Message -
>> From: "Kirk Wallace" <[EMAIL PROTECTED]>
>> To: "Enhanced Machine Controller (EMC)" 
>> ;
>> <[EMAIL PROTECTED]>
>> Sent: Sunday, February 03, 2008 4:13 AM
>> Subject: Re: [Emc-users] Modbus RS-485 Transceiver
>>
>>
>>> On Sun, 2008-02-03 at 18:12 +1100, Peter Homann wrote:
>>>> Hi Kirk,
>>>>
>>>> A couple of things.
>>>>
>>>> The ModIO I sent you has a RS232-485 converter built in. With this you
>>>> can run
>>>> a serial cable from the ModIO to the PC, then run additional Modbus
>>>> devices
>>>> from the RS485 terminals on the ModIO. It saves from needing an 
>>>> external
>>>> converter.
>>>>
>>>> When using RS485 I recommend using full duplex rather than 1/2 duplex.
>>>> Some
>>>> times there are issues with buffers in the PC and timing for switching
>>>> the
>>>> transmission direction
>>>>
>>>> Cheers,
>>>>
>>>> Peter.
>>>
>>> I'm looking forward to getting my hands on it.
>>>
>>> Since I don't know what I am doing yet, I was thinking that I could try
>>> to address the timing issues. Is it that the serial port uses internal
>>> buffers, so you don't know exactly when data will be sent and due to the
>>> query and response nature of Modbus, the timing is important? I seem to
>>> recall that some parallel ports had the same problem, but the driver was
>>> broken, which disabled the buffer, so ports with fifo's were okay to use
>>> with EMC. I wonder if the buffers on the serial port could be disabled
>>> too. It would be nice to be able to use Modbus in its common forms. But
>>> since you have covered this territory, you could probably talk some
>>> sense into me.
>>>
>>> --
>>> Kirk Wallace (California, USA
>>> http://www.wallacecompany.com/machine_shop/
>>> Hardinge HNC lathe,
>>> Bridgeport mill conversion, doing XY now,
>>> Zubal lathe conversion pending)
>>>
>>>
>>> --

Re: [Emc-users] Modbus RS-485 Transceiver

[Peter C. Wallace]

On Sun, 3 Feb 2008, Javid Butler wrote:

> Date: Sun, 3 Feb 2008 08:27:42 -0600
> From: Javid Butler <[EMAIL PROTECTED]>
> Reply-To: "Enhanced Machine Controller (EMC)"
> 
> To: "Enhanced Machine Controller (EMC)" 
> Subject: Re: [Emc-users] Modbus RS-485 Transceiver
> 
> Kirk-
>
> With half duplex EIA-485 timing is very important. Unlike Ethernet, EIA-485
> does not support collision detection at the physical layer so collisions
> between outgoing data and returning data cause data corruption, since the
> trancievers do not back off and retransmit. After a query the controller has
> to release the line and allow the responder to talk.
>
> You will probably have to watch flow control. For what you want to do the
> controller should transmit a query and then immediately tri-state, but
> converting from EIA-232 it may hold the line high or low, perhaps
> anticipating the next transmission. You might have to work with the way
> messages are buffered-perhaps you will only be able to buffer one message at
> a time.
>
> Javid



Even without buffering you still need to wait until the character has been 
shifted out of the UARTs transmit shift register before line-turnaround. You 
can do this by polling TBE and TSRE but you would have to poll fast enough to 
meet the minimum response time of the Modbus peripheral. A better way is to 
use a more advanced serial chip (Exar,OxfordSemi,NetMos) that includes RS-485 
support. There are also some RS-232/RS-485 adapters that use a one-shot to 
enable the RS-485 Xmit enable, a little Mickey-Mouse but maybe ok at low baud 
rates.

As someone else posted, full duplex links avoid the timing problem altogether.

  > >
> - Original Message -
> From: "Kirk Wallace" <[EMAIL PROTECTED]>
> To: "Enhanced Machine Controller (EMC)" ;
> <[EMAIL PROTECTED]>
> Sent: Sunday, February 03, 2008 4:13 AM
> Subject: Re: [Emc-users] Modbus RS-485 Transceiver
>
>
>> On Sun, 2008-02-03 at 18:12 +1100, Peter Homann wrote:
>>> Hi Kirk,
>>>
>>> A couple of things.
>>>
>>> The ModIO I sent you has a RS232-485 converter built in. With this you
>>> can run
>>> a serial cable from the ModIO to the PC, then run additional Modbus
>>> devices
>>> from the RS485 terminals on the ModIO. It saves from needing an external
>>> converter.
>>>
>>> When using RS485 I recommend using full duplex rather than 1/2 duplex.
>>> Some
>>> times there are issues with buffers in the PC and timing for switching
>>> the
>>> transmission direction
>>>
>>> Cheers,
>>>
>>> Peter.
>>
>> I'm looking forward to getting my hands on it.
>>
>> Since I don't know what I am doing yet, I was thinking that I could try
>> to address the timing issues. Is it that the serial port uses internal
>> buffers, so you don't know exactly when data will be sent and due to the
>> query and response nature of Modbus, the timing is important? I seem to
>> recall that some parallel ports had the same problem, but the driver was
>> broken, which disabled the buffer, so ports with fifo's were okay to use
>> with EMC. I wonder if the buffers on the serial port could be disabled
>> too. It would be nice to be able to use Modbus in its common forms. But
>> since you have covered this territory, you could probably talk some
>> sense into me.
>>
>> --
>> Kirk Wallace (California, USA
>> http://www.wallacecompany.com/machine_shop/
>> Hardinge HNC lathe,
>> Bridgeport mill conversion, doing XY now,
>> Zubal lathe conversion pending)
>>
>>
>> -
>> This SF.net email is sponsored by: Microsoft
>> Defy all challenges. Microsoft(R) Visual Studio 2008.
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>>
>
>
>
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Peter Wallace
Mesa Electronics

(\__/)
(='.'=) This is Bunny. Copy and paste bunny into your
(")_(") signature to help him gain world domination.


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Re: [Emc-users] Modbus RS-485 Transceiver

[Javid Butler]

Kirk-

With half duplex EIA-485 timing is very important. Unlike Ethernet, EIA-485 
does not support collision detection at the physical layer so collisions 
between outgoing data and returning data cause data corruption, since the 
trancievers do not back off and retransmit. After a query the controller has 
to release the line and allow the responder to talk.

You will probably have to watch flow control. For what you want to do the 
controller should transmit a query and then immediately tri-state, but 
converting from EIA-232 it may hold the line high or low, perhaps 
anticipating the next transmission. You might have to work with the way 
messages are buffered-perhaps you will only be able to buffer one message at 
a time.

Javid


- Original Message - 
From: "Kirk Wallace" <[EMAIL PROTECTED]>
To: "Enhanced Machine Controller (EMC)" ; 
<[EMAIL PROTECTED]>
Sent: Sunday, February 03, 2008 4:13 AM
Subject: Re: [Emc-users] Modbus RS-485 Transceiver


> On Sun, 2008-02-03 at 18:12 +1100, Peter Homann wrote:
>> Hi Kirk,
>>
>> A couple of things.
>>
>> The ModIO I sent you has a RS232-485 converter built in. With this you 
>> can run
>> a serial cable from the ModIO to the PC, then run additional Modbus 
>> devices
>> from the RS485 terminals on the ModIO. It saves from needing an external
>> converter.
>>
>> When using RS485 I recommend using full duplex rather than 1/2 duplex. 
>> Some
>> times there are issues with buffers in the PC and timing for switching 
>> the
>> transmission direction
>>
>> Cheers,
>>
>> Peter.
>
> I'm looking forward to getting my hands on it.
>
> Since I don't know what I am doing yet, I was thinking that I could try
> to address the timing issues. Is it that the serial port uses internal
> buffers, so you don't know exactly when data will be sent and due to the
> query and response nature of Modbus, the timing is important? I seem to
> recall that some parallel ports had the same problem, but the driver was
> broken, which disabled the buffer, so ports with fifo's were okay to use
> with EMC. I wonder if the buffers on the serial port could be disabled
> too. It would be nice to be able to use Modbus in its common forms. But
> since you have covered this territory, you could probably talk some
> sense into me.
>
> -- 
> Kirk Wallace (California, USA
> http://www.wallacecompany.com/machine_shop/
> Hardinge HNC lathe,
> Bridgeport mill conversion, doing XY now,
> Zubal lathe conversion pending)
>
>
> -
> This SF.net email is sponsored by: Microsoft
> Defy all challenges. Microsoft(R) Visual Studio 2008.
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Re: [Emc-users] Modbus RS-485 Transceiver

[Kirk Wallace]

On Sun, 2008-02-03 at 18:12 +1100, Peter Homann wrote:
> Hi Kirk,
> 
> A couple of things.
> 
> The ModIO I sent you has a RS232-485 converter built in. With this you can 
> run 
> a serial cable from the ModIO to the PC, then run additional Modbus devices 
> from the RS485 terminals on the ModIO. It saves from needing an external 
> converter.
> 
> When using RS485 I recommend using full duplex rather than 1/2 duplex. Some 
> times there are issues with buffers in the PC and timing for switching the 
> transmission direction
> 
> Cheers,
> 
> Peter.

I'm looking forward to getting my hands on it.

Since I don't know what I am doing yet, I was thinking that I could try
to address the timing issues. Is it that the serial port uses internal
buffers, so you don't know exactly when data will be sent and due to the
query and response nature of Modbus, the timing is important? I seem to
recall that some parallel ports had the same problem, but the driver was
broken, which disabled the buffer, so ports with fifo's were okay to use
with EMC. I wonder if the buffers on the serial port could be disabled
too. It would be nice to be able to use Modbus in its common forms. But
since you have covered this territory, you could probably talk some
sense into me.

-- 
Kirk Wallace (California, USA
http://www.wallacecompany.com/machine_shop/ 
Hardinge HNC lathe,
Bridgeport mill conversion, doing XY now,
Zubal lathe conversion pending)


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Re: [Emc-users] Modbus RS-485 Transceiver

[Kirk Wallace]

On Sun, 2008-02-03 at 03:06 -0500, Dean Hedin wrote:
> Interesting if you have the time..
> 
> But for six bucks and free shipping...
> http://www.dealextreme.com/details.dx/sku.6040

Obviously, I didn't look hard enough when went looking for these. Thanks
for the link Dean.

-- 
Kirk Wallace (California, USA
http://www.wallacecompany.com/machine_shop/ 
Hardinge HNC lathe,
Bridgeport mill conversion, doing XY now,
Zubal lathe conversion pending)


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Re: [Emc-users] Modbus RS-485 Transceiver

[Dean Hedin]

Interesting if you have the time..

But for six bucks and free shipping...
http://www.dealextreme.com/details.dx/sku.6040

- Original Message - 
From: "Kirk Wallace" <[EMAIL PROTECTED]>
To: "Enhanced Machine Controller (EMC)" 
Sent: Saturday, February 02, 2008 11:26 PM
Subject: [Emc-users] Modbus RS-485 Transceiver


> Chris Morley, 
> 
> I have been pretty slow with work on Modbus. I just read your wiki post
> and you indicated that you needed an RS-485 adapter. I found one here:
> 
> http://pinouts.ru/SerialPortsCables/rs485_cable_pinout.shtml
> 
> I plan on building a couple for my SJ200 application, and if you want I
> can make an extra and send it over. I'm not sure when I'll have time to
> build and test it -- probably in the next couple of weeks. Let me know.
> 
> -- 
> Kirk Wallace (California, USA
> http://www.wallacecompany.com/machine_shop/ 
> Hardinge HNC lathe,
> Bridgeport mill conversion, doing XY now,
> Zubal lathe conversion pending)
> 
> 
> -
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> Defy all challenges. Microsoft(R) Visual Studio 2008.
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Re: [Emc-users] Modbus RS-485 Transceiver

[Peter Homann]

Hi Kirk,

A couple of things.

The ModIO I sent you has a RS232-485 converter built in. With this you can run 
a serial cable from the ModIO to the PC, then run additional Modbus devices 
from the RS485 terminals on the ModIO. It saves from needing an external 
converter.

When using RS485 I recommend using full duplex rather than 1/2 duplex. Some 
times there are issues with buffers in the PC and timing for switching the 
transmission direction

Cheers,

Peter.

Kirk Wallace wrote:
> Chris Morley, 
> 
> I have been pretty slow with work on Modbus. I just read your wiki post
> and you indicated that you needed an RS-485 adapter. I found one here:
> 
> http://pinouts.ru/SerialPortsCables/rs485_cable_pinout.shtml
> 
> I plan on building a couple for my SJ200 application, and if you want I
> can make an extra and send it over. I'm not sure when I'll have time to
> build and test it -- probably in the next couple of weeks. Let me know.
> 

-- 
--
Web:   www.homanndesigns.com
email: [EMAIL PROTECTED]
Phone: +61 421 601 665
www.homanndesigns.com/ModIO.html - Modbus Interface Unit
www.homanndesigns.com/DigiSpeedDeal.html - DC Spindle control
www.homanndesigns.com/TurboTaig.html - Taig Mill Upgrade board

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[Emc-users] Modbus RS-485 Transceiver

[Kirk Wallace]

Chris Morley, 

I have been pretty slow with work on Modbus. I just read your wiki post
and you indicated that you needed an RS-485 adapter. I found one here:

http://pinouts.ru/SerialPortsCables/rs485_cable_pinout.shtml

I plan on building a couple for my SJ200 application, and if you want I
can make an extra and send it over. I'm not sure when I'll have time to
build and test it -- probably in the next couple of weeks. Let me know.

-- 
Kirk Wallace (California, USA
http://www.wallacecompany.com/machine_shop/ 
Hardinge HNC lathe,
Bridgeport mill conversion, doing XY now,
Zubal lathe conversion pending)


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