serial ports

[richerdick]

is there a reliable way to get over the problem that most new laptops have no serial ports, does anyone have any experiences with the pcmcia card ports? or usb to serial converters
thanks

 

[TWControls]

Part of the answer to the question is going to depend on what all you have to communicate with. I use a Belkin USB to Serial adapter and have had great success with it. But it still doesn't work for everything. For instance the 1747-PIC module for AB RS-485/DH-485 does not work with it. So for that I use the 1747-UIC.

I wouldn't get too settled with a PCMCIA solution since the have also been obsoleted and replaced with the PciExpress Card.

In my opinion the best thing to do is select a USB to Serial adapter that is compatible with your existing equipment and make all new equipment with a Ethernet interface.

I say Ethernet instead of USB because who knows how long before USB is obsoleted.

Just my 2 cents
TW

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[richs]

"make all new equipment with a Ethernet interface."

That's a considerable increase in hardware requirements and
quite a bit of extra software putting the stack on an
embedded application.

I'm not trying to start a flame war or anything, but since
we are in the PLC forum, I think a good interface to rs485
would be in order.

MAYBE, an ethernet to rs485 translator would be more the
thing to have. You could "dongle" that (I believe that there
is off the shelf hardware, but no software) for that sort
of thing.

OR, the TI development package for their new little micro
comes as a header that slips into their proprietrary
usb plug.

The other thing, since we are here in PLC land, I'm sure
that laptops are not the computing devices of choice for
most factory SCADA applications with desktops being the
platform of choice.

Downloading new PLC apps, temp. collection of data, I can
see using the laptop, but not for day to day operations.
Therefore, a suitable PCI rs232/rs485 interface card
would be the likely choice.

These are just MY 2 cents worth.

Cheers,

Rich S.

 

[dpc]

There is no fool-proof method that works 100%, in my painful experience. The USB-serial converters are the obvious first try, but some poorly-written software (and Windows) conspire to make it impossible to select the COM port that the USB gadget ends up with.

There are PCMCIA cards that provide serial ports - these are reported to work a little better according to some relay technicians I know.

It's going to depend on your legacy software, the USB-Serial converter drivers and your operating system.

In my experience, problems generally occur in the field, in the rain, at night, with four or five impatient electricians looking over my shoulder. It's always good to try it out ahead of time, if possible.

 

[ScottyUK]

Personally I like Ethernet for fast, cheap, low cost, almost infallible connection. All you need is either a fixed IP address or a DNS. Hardware is common as dirt and almost as cheap. The capability to use long cables and wireless or fibre are invaluable, especially when it lets you work in the dry and warm with working light while debugging that PLC out on site instead of being soaking wet and cold in the dark.

Serial's big downfall to me is that it is so damned flexible with so many different configurable options that in dpc's world - which I also seem to live in - it will find a way to go wrong at the most inconvenient time imaginable: maybe you won't have all the config information to hand or maybe the port is still configured for some other bit of equipment you were working on; maybe it needs a null modem connection, or maybe not. Which of the six different serial cables is the right one? 25 pin or 9 pin? Where's that bloody gender bender?? DCE or DTE? Does it have a parity check? How many data bits? One stop bit or two?

And that is just RS-232 itself without the complication brought about by the half-hearted support in later versions of Windows and the equally dismal efforts by PC manufacturers and particularly laptop manufacturers to implement a full spec serial port. I may have a wry smile when I remember serial in years to come, but I won't miss it.


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Sometimes I only open my mouth to swap feet...

 

[TWControls]

"That's a considerable increase in hardware requirements and
quite a bit of extra software putting the stack on an
embedded application."

With almost all of the manufacturers now making or in the development a small PLC with built in Ethernet such as the Micrologix 1100 there is no excuse for small applications not being able to connect to Ethernet.

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http://www.twcontrols.com

 

[dpc]

I agree that Ethernet is the future, but there are a lot of legacy relays, PLCs, etc out there with only a serial port.

There are also these little guys:

http://www.selinc.com/sel-2890.htm

 

[TWControls]

Thanks for the link. Looks like a nice product

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[richs]

Hi-

Guess it's a matter of degree. DPC mentions:

http://www.selinc.com/sel-2890.htm

and they quote $400.00. Not cheap in my book!

One could cobble up an ethernet enabled micro for about $50.00 or so. Reference:

http://www.sparkfun.com/commerce/product_info.php?products_id=7829#

Still, that's not inexpensive.

The only reason that we get really inexpesive ethernet PCI
cards is due to the very volume of the boards that are
made. Also, it has to be backed up with the PC's
extensive RAM and cpu speed.

ScottyUK mentions the "ease" of ethernet cables. I worked
for Cisco for awhile. In our lab, we had bins and bins
of ethernet cables. In the lab, it's fine. Out on the
floor? Well, that might be a different situation. I've
had my share of problems with ethernet cables (and
connectors). Did I need a one to one, or a crossover
cable? Did somebody bust off the retaining tab from the
cable and is it riding in the socket on a wing and a
prayer? Patch panels tend to degrade into indecipherable
rat's nests, even with the best of documentation and
even better intentions. And the RJ45 connectors are not
really designed to be outside of an office environment.

Finally, the more "interesting" situations:
1. How close to the 100Meter limit is the cable running?
2. Contamination of the cable and how will it reflect
for collision avoidance?
3. How many levels on the hubs? Did the hub die?
4. The same as #3 for switches.
5. Traffic already on the lan?
6. Duplicate IP addresses. Or DHCP servers dropping leases?
7. Dynamic routing protocols.
8. Viruses. O.K. now I've scared myself.
I'm stopping here.

These are the real toughies to solve.

And the ethernet frame with the TCP/IP packet usually
associated with it and one could find that the overhead
of the packet far exceeds the payload of the packet.

Don't get me wrong. I'm quite a fan of ethernet in LAN's
and non hostile environments. Don't even mind them doing
"mission critical" operations.

And, since I'm coming from the other side of the equasion,
one more on the equipment supplier side, if you guys
want ethernet, and don't mind paying the price, sure
there will be one of us that will be glad to have an
RJ45 socket on the critters we supply you with.

As a side issue, this was something that I was thinking
about today. If you guys are using ethernet, are you
also using simple network management protocol (SNMP)?
One could easily populate the "experimental" portions
of the MIB with their custom devices and use some of the
existing tools (like MRTG or RRD) for data collection
and presentation? Traps and snmpsets for process
control? Granted SNMP was designed to monitor and
control computer networks (and nodes), but the framework
is all there.

Just curious.

Again, not trying to start a flame war, just my thoughts.


Cheers,

Rich S.

 

[TWControls]

Sorry Richs but you've completely lost me on this one. You can now purchase PLCs with built in Ethernet for the same price as serial processors. Where's the additional expense in putting Ethernet based PLCs in new equipment? I can buy the PLC with the built in Ethernet for less than $400.

Don't forget when you were quoting me it was in reference to new equipment. I just appreciated DPC's link because I have a project I'm looking into that it would work on.

Also how do you solve the original posters of lack of a serial port. PCMCIA is also not an option for long since it is being obsoleted. The only two options I'm seeing are USB and Ethernet. Do you have a third option to suggest that would help the original poster or are you just trying to start a flame war? If you are just wanting to start a flame war just say so and I'll walk away and give you the thread. I've got better things to do.

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http://www.twcontrols.com

 

[richs]

TWControls

I *SPECIFICALLY* don't want to start a flame war. Please
review my posts.

As to the OP, well, that's been pretty much covered already.

Cheers,

Rich S.

 

[ScottyUK]

Hi Rich,

ScottyUK mentions the "ease" of ethernet cables. I worked for Cisco for awhile. In our lab, we had bins and bins of ethernet cables. In the lab, it's fine. Out on the floor? Well, that might be a different situation. I've had my share of problems with ethernet cables (and connectors). Did I need a one to one, or a crossover cable? Did somebody bust off the retaining tab from the cable and is it riding in the socket on a wing and a prayer? Patch panels tend to degrade into indecipherable rat's nests, even with the best of documentation and even better intentions. And the RJ45 connectors are not really designed to be outside of an office environment.

Fair points. Taking them in turn:

I've rarely, if ever, seen a crossover used anywhere except uplinks or direct connection of two computers. I'm pretty sure I've not seen it on automation equipment. I hope the jokers at A-B don't decide to introduce one just so they can sell an A-B badged cable especially for their equipment at a hugely inflated price!

The missing tab is definitely a pain in the neck but least it is a visible pain in the neck!

Patch panels are a mess because IT people are untidy creatures. At least, ours are.

Most automation equipment is normally in a reasonably clean, dry, warm environment if the panel was designed and installed properly. The worst I've done was step on the RJ45 connector which was easily rectified by swapping the cable or another standard Cat 5 patch lead. Minimal downtime - most of my serial leads are either vendor specials or ones I've made myself because I won't pay vendor prices. Downtime either way is longer.


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Sometimes I only open my mouth to swap feet...

 

[richs]

Yeah-

I guess upon review the two areas that I'm grumbling about
are:

1. I seen the "deevolution" of ethernet from the early DARPA
days, going from the fat old coax, to the thin coax,
to 10BaseT. I guess that's a good thing in some respects.
No dealing with MAUs anymore and tons of BNC tees
running around. But at the sacrafice of sheilding and
"crimp on" connectors.

2. The relative cost of the speed and overhead. And I'm
going to "lump in" the TCP/IP stack in this section.
10BaseT (to pick the slowest of the common networks
today) is 10MBits/sec. That's a screaming lots of
information possible for something like an integer
or real variable, or small set of variables. Second
in this "grumble" is again with the small amount of
data that is being passed. Most of the frame will be
taken up with the frame format, not the data itself.
for the TCP/IP stuff (and the Datagram stuff), this
kind of makes sense. The frame was designed to be
transmitted out of sequence, through various paths,
and unknown quality of service (qos) from nodes spanning
thousands of miles. All this computational power
where to my way of thinking, a simple master/slave
with station address, command/response status, payload
and error correcting/detecting frame seems to be more
"data for the bits".

But, whatever. I guess I should be glad. Ethernet is a
pretty well know entity for me. If the industry is going
that way, well, it's less for me to learn.

Cheers,

Rich S.

 

[richerdick]

thanks for the comments but in referal to my original question. If i can get a usb to serial interfae to communicate is this likely to be a reilable link iewhen down loading to plcs drives etc am i likely to get any corruption that i wouldnt have got just using a standard serial port

 

[TWControls]

Yes, sorry the thread seemed a turn that was not helpful for you. Going back to my original response, it would be good to know what PLCs you will need to connect to.

Personally I use an older Belkin FSU103. I can connect will all Allen Bradley PLCs running DF1, DF1 Panelviews, Mitsubishi, Compumotor, in fact it has worked on everything I can think of except RS232 ports running DH485. Without getting too technical pretty much the USB adapters can only do software switching and DH485 requires hardware switching.

But it would be best if you told us what you currently have to connect to. For future projects you need to start thinking about an alternative to the serial connection

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http://www.twcontrols.com

 

[fornhamspark]

In Answer to the question just buy a laptop with serial port. I know they are hard to find but i now use Dell Laptops that have serial as standard. And the new laptop even has convered ports, splashproof keyboard and view in the daylight screen. Note at the fraction of the cost of a Panasonic toughbook.

 

[ScottyUK]

richerdick,

Allen Bradley's 1747-UIC is the first reliable, affordable interface they have ever produced for interfacing to the SLC5 series from a laptop other than a plain serial cable for certain processors. As a former user of the dreadful 1747-PIC I can give A-B a little pat on the back for their latest offering.

Hopefully others will chip in with their experiences and answer your question now we've decided that Ethernet is the true way forward!

Fornhamspark,

Is it a full spec serial port or is it power-limited? Certain interfaces (e.g. my old enemy the 1747-PIC) draw power from the port and modern ports just don't supply enough for the interface to work reliably. I think this is part of the reason why the PIC doesn't work with USB converters, the other part being the custom serial driver A-B used. Power-saving software sometimes reduces port power even further, depending on how it is implemented. I'm almost sure Compaqs of a certain vintage did this: it gives rise to puzzling results where things work fine when the laptop is on mains power but refuse to work on battery.


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Sometimes I only open my mouth to swap feet...

 

[Skogsgurra]

I put a powered hub in-between. Got myself three more USB ports and more punch, too. But, yes, some things will never work again (unless I dig out that old Windows 95 laptop and get a new battery for it).

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ScottyUK]

Ha-ha, you're in modern times with Win 95! I have a 2.8Ghz Pentium II running DOS 6.22 and Windows 3.11 as one boot option, along with NT4 and XP. I will probably put Linux or Solaris 10 i86 on the last partition eventually. Communication with the engineering antiques I need to support works better when the old DOS application runs in its native O/S instead of the pseudo-DOS command line in later versions of Windows.

How many people use Virtual Machine operating system emulation? My IT guys want me to try it and I want to keep my multi-boot machine with three or four operating systems: am I a Luddite?


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Sometimes I only open my mouth to swap feet...

 

[TWControls]

Scotty, I'm just getting into using Virtual Machines. They are great!!!

I also use the 1747-UIC for DH-485 connections. I was holding back on saying that until Richerdick got into what connections he needed. The 1747-UIC is for DH-485 connections over RS232 and RS485. IT WILL NOT DO DF1.

Also, the old 1747-PIC is not compatible with any of the USB to Serial adapters that I am aware of. Not only the device, but the driver that is used to do DH485 over RS232. With a "Real" serial port you could just switch driver between DF1 and DH485 over RS232. With USB to Serial adapters and many new computers with "built in" serial ports this is no longer possible. DH485 requires hardware switching which these newer serial devices can't do. They will only do DF1 for AB. As Scotty led onto, laptops with "REAL" serial ports are getting very hard to find. Laptops with "built in" serial ports are becoming more common and will not work with many PLCs and PLC interfaces. That's why I quit recommending people search for laptops with built in serial ports.

AB now also offers a USB to Serial Adapter for DF1. If all you connect to is AB then this is a reasonable interface to purchase. But if you are connecting to different brands I doubt the others are going to help you connect to their PLCs with an AB interface even if it would work. I haven't played with that one yet so I don't know

Bottom line Richerdick, we need to know more about what you must connect with to make a good decision. For a guess, I would go with the Belkin USB to serial adapter. It has worked well for me but I have no proof it will work in your applications as well.

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http://www.twcontrols.com