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Old December 29th, 2017, 12:51 PM   #1
strantor
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What is it about some applications that require a physical COM port?

In the distant past I was involved in troubleshooting a wide array of PLCs from all MFGs, ranging from brand new to fossilized. I remember there were some PLCs (esp older Allen Bradley if I remember correctly) that you could not connect to them via a USB->Serial converter; had to be a physical COM port.

For the past 4 years I have been dealing with nothing but brand-new Omron PLCs which are interfaced with using a straight USB cable. Now I'm getting back into my old line of work and looking to purchase a new laptop for that purpose. I'm looking for a brand new laptop with a physical COM port and apparently that's a unicorn.

So it makes me wonder exactly what is it about some applications that require a physical COM port? Is the software doing some kind of strange thing with the pin voltages that only a physical port can do?

And 2 related questions:
1. Are there any brand-new laptops today, with a physical COM port?
2. Have there been any USB-Serial converters to come out in the last few years which can replace a physical COM port in every way, and interface with these old PLCs?
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Old December 29th, 2017, 01:00 PM   #2
danw
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The pre-NT/2000/XP/7/10 O/S's, that is DOS/3/95/98, controlled the serial COM ports differently than the later MS O/S's. I'm straining to remember details and I'm coming up blank. NT might have been a grey area, I can't recall.

The effect was that software apps using serial com ports designed for DOS/3/95/98 would not work in the NT-forward O/S's.

I do know that I've had excellent performance from USB/232 converters that use the FTDI chipset in XP and 7. But I rarely, if ever, deal with DOS/3/95/98 era stuff.
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Old December 29th, 2017, 01:01 PM   #3
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Get one of these:
https://www.plccable.com/usb-to-rs23...l-plctalk-net/

You might run into a rare case where the above cable won't work but all of the hardware I have dealt with so far has worked with it.

I can also recommend this kit for most all A/B PLCs:
https://www.plccable.com/allen-bradl...ogramming-set/

It includes a DH-485 cable and cables/adapters for the Micrologix round 8 pin connector.

I have used the DH485 cable with old Panelviews and the SLC 5/03 with no problems.

I can't answer in good detail your specific questions about the real serial port except that I understand it to be an issue with timing, not voltages.
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Old December 29th, 2017, 01:07 PM   #4
strantor
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Quote:
Originally Posted by danw View Post
The pre-NT/2000/XP/7/10 O/S's, that is DOS/3/95/98, controlled the serial COM ports differently than the later MS O/S's. I'm straining to remember details and I'm coming up blank. NT might have been a grey area, I can't recall.

The effect was that software apps using serial com ports designed for DOS/3/95/98 would not work in the NT-forward O/S's.

I do know that I've had excellent performance from USB/232 converters that use the FTDI chipset in XP and 7. But I rarely, if ever, deal with DOS/3/95/98 era stuff.
I never used DOS for PLC programming, whatever the issues I was experiencing in the past (which I also strain to remember, exactly what the issues were) I was using WIN7 and/or XP.
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Old December 29th, 2017, 01:13 PM   #5
undr_the_table
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you'll probably have to build the laptop look for motherboards with rs232 ports if you want one with a built in RS232 port :
https://www.directron.com/efika.html...CABEgJmUvD_BwE these motherboard types are still available although considered legacy,

it may be that these controllers had more than just RS232 on that port if it had 422 and you were to pass a signal there it would stop comms, I would look at the programming cable pinout and the pinout of the controller to make sure
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Old December 29th, 2017, 01:18 PM   #6
strantor
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Quote:
Originally Posted by OkiePC View Post
Get one of these:
https://www.plccable.com/usb-to-rs23...l-plctalk-net/

You might run into a rare case where the above cable won't work but all of the hardware I have dealt with so far has worked with it.

I can also recommend this kit for most all A/B PLCs:
https://www.plccable.com/allen-bradl...ogramming-set/

It includes a DH-485 cable and cables/adapters for the Micrologix round 8 pin connector.

I have used the DH485 cable with old Panelviews and the SLC 5/03 with no problems.

I can't answer in good detail your specific questions about the real serial port except that I understand it to be an issue with timing, not voltages.
Thanks for the links. Those looked familiar so I pulled out my old funbag of cables, and I already have that 1747-UIC kit. Still in the box, wrapped in plastic; I don't think I've ever used it. I guess if that specific Allen Bradley need arises, I have that one covered.

I cited one specific (Allen Bradley) scenario where a physical COM port was required, and that one's been crossed off now, but I remember there were more scenarios than just that one. I can't recall what they were though. I want to say there were some old Servo drives that gave me trouble.

I would be happy as a clam if there were some (USB/Ethernet/Other) device that were guaranteed to do be able to do everything a physical COM port can do (Or find a laptop with a COM port), so that I can take that into the field with me and always rest easy that whatever I come across, no matter what it is or if I've ever heard of it before, I will be able to talk to it.
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Old December 29th, 2017, 01:21 PM   #7
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Quote:
Originally Posted by undr_the_table View Post
you'll probably have to build the laptop look for motherboards with rs232 ports if you want one with a built in RS232 port :
https://www.directron.com/efika.html...CABEgJmUvD_BwE these motherboard types are still available although considered legacy,

it may be that these controllers had more than just RS232 on that port if it had 422 and you were to pass a signal there it would stop comms, I would look at the programming cable pinout and the pinout of the controller to make sure
To be honest I didn't even know that you could build your own laptop. I've built plenty of desktops but my laptop hardware experience has been limited to upgrading RAM, replacing HDD, and replacing cracked screens. I'll look into it. Thanks for the tip.
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Old December 29th, 2017, 02:58 PM   #8
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I use the 1747-UIC every once in a while with no issues.

Have used the keyspan USA-19HS USB to serial converter for many years with no issues.
Only one I use because it has worked so well for me.
https://www.tripplite.com/keyspan-hi...apter~USA19HS/


FYI running Windows 7 Professional

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Old December 29th, 2017, 03:11 PM   #9
Gene Bond
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I recall that in DOS (Win 3x, 95, 98, ME), you could manipulate the hardware directly rather than us MS's device driver... Therefore some did, and caused the issue you are running into. In DOS, you had to 'roll your own driver', so you are pretty much SOL to run it through a USB converter.

I know I had a few old Win 3x programs that ran OK through my Keyspan converter on XP, but I haven't tried them yet since switching to Win 10 (which sucks). Not sure about 7 or 8, since I skipped them.
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Old December 29th, 2017, 03:24 PM   #10
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Quote:
Originally Posted by jimtech67 View Post
I use the 1747-UIC every once in a while with no issues.

Have used the keyspan USA-19HS USB to serial converter for many years with no issues.
Only one I use because it has worked so well for me.
https://www.tripplite.com/keyspan-hi...apter~USA19HS/


FYI running Windows 7 Professional

I also have a Keyspan USA-19HS and it works well with all but one device I have ever tried it with.

I have begun to prefer the one from PLCCable simply for mechanical reasons. It has a nice long cable and stays where I put it whereas the Keyspan has that USB type A connection that can come loose. The Keyspan does include some handy utilities that I like though.

It is probably a good idea to have more than one brand of converter in your bag. I think I have 4 unique types of USB-RS232 converters.
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Old December 29th, 2017, 03:40 PM   #11
Steve Bailey
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Quote:
I would be happy as a clam if there were some (USB/Ethernet/Other) device that were guaranteed to do be able to do everything a physical COM port can do (Or find a laptop with a COM port), so that I can take that into the field with me and always rest easy that whatever I come across, no matter what it is or if I've ever heard of it before, I will be able to talk to it.
As Hemingway said, "Isn't it pretty to think so", but I think its a pipe dream.
My client base was not huge and a significant percentage of it was GE gear. Even so, I was never able to consolidate on a single set of components to cover all serial communications needs.
The last laptop I purchased with a serial port is a Dell Latitude running Windows XP. That's my go-to for situations when I know the USB/serial converter won't work. The one in particular is to send a modified configuration to a GE VersaMax Genius network interface module. It's also the one I fire up when I just need to open a Series One or Series Six project using Logicmaster One or Logicmaster Six. Even then I need to run those apps under DOSbox.
When I actually have to connect to a Series One, Series Five or Series Six I have an old DOS computer with a 386 CPU.
The USB/serial converter I used to use with the XP machine came from Radio Shack and it served me well. But they discontinued it and never came out with drivers for Windows 7 so its useless with newer laptops. Fortunately, the converter from Staples has worked with everything I need it to. For those things that are RS485 only the converter from B&B works.
Generally when I leave the office to go to a customer's site, I know what I'll need and bring the necessary laptop, cables, and converters. If I'm not sure, I have serial cables with pigtail leads on one end and D-sub to terminal adapters so I can quickly come up with a custom serial cable.
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Old December 29th, 2017, 03:49 PM   #12
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A bit expensive but I would go the serial to Ethernet port server route. I have never had any issues with any serial device. It is also so great that I can drop the port server in a control panel and if there is Ethernet there I can connect anywhere in the plant where it is quite and better working conditions. I have used systech and digi units. You can find them cheap on Ebay used I have bought multiple units and never had a bad one. Another big plus is you can find units that have multiple ports. With the systech units they apply directly to the IQR on the pc. It is looked at as a real serial port in the hardware configuration.
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Old December 29th, 2017, 04:40 PM   #13
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USB or ethernet to serial can't get the same tight timing as you can with a standard serial port. It's especially true for application using the control signals on the port (CTS/RTS/DCD etc). I think you can find laptops with serial ports today as well, but you have to look for industrial laptops.

My old laptop had a serial port but I bought that a couple of years ago. Nowadays I just bring a small embedded industrial PC when I need something with a real serial port. It's very common to have that on those.
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Old December 29th, 2017, 04:44 PM   #14
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Quote:
Originally Posted by strantor View Post
1. Are there any brand-new laptops today, with a physical COM port?
It may not be easy to find a new laptop with a physical COM port, but it is fairly easy to find laptops with the port that will allow you to add a physical COM port. An example would be a laptop with an ExpressCard slot and using one of these:

https://www.startech.com/Cards-Adapt...0-UART~EC1S952
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Old December 29th, 2017, 04:56 PM   #15
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Originally Posted by Archie View Post
It may not be easy to find a new laptop with a physical COM port, but it is fairly easy to find laptops with the port that will allow you to add a physical COM port. An example would be a laptop with an ExpressCard slot and using one of these:

https://www.startech.com/Cards-Adapt...0-UART~EC1S952
That's a good point! I forgot all about that even if I did that myself not that many years ago. I had a smaller card with a special cable that had the 9-pin d-sub on the other end.

Good thing was that you could have the card mounted all the time because it didn't stick out. Bad thing was that you had to make sure to bring the special serial cable.

PS. There is also the possibility to use the mini-pcie port available inside many modern laptops. There are serial mini-pcie cards available. Just more of a hack because you need to figure out how to get the dsub connector out.

Last edited by Pete.S.; December 29th, 2017 at 05:02 PM.
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