Functioning Serial Ports on New Laptops

[Mtn_Bkng_Dave]

Laptops

I have been listening to this debate for many years now.
As of yet I have not run across this problem.

I only run Dell systems and have so for about as long as they have been in business.

The trick I have found is to not buy a "laptop" but rather a "mobile desktop". It will cost you a few pounds in weight but offers all the full featured functionality we have come to expect.

My current system has Serial, Parallel, Firewire, 10/100 Enet, Wireless Enet, and Modem built in. Check out the high end Inspiron series for more information. The cheaper Latitude series suffers the same issues you have discussed.

As far as serial compatibility......I run all versions of my programming packages currently on WinXP. This includes the older direct serial port access programs such as the SLC version 3 interface.

The trick to making these work is to create a shortcut to the program.
Under properties you can click the compatibility mode tab. Set it to run in WIndows 95 compatability mode and the serial issue is gone. This allows the program to directly access the port. Normal NT based windows operation is to allow the OS to manage the port. This WILL NOT work for older dos based software or early 16 bit windows packages.

I am yet to find one that will not work with this method.

Hope this helps,

Dave

 

[Foghorn22]

We are replacing the RS232 port on our latest product with USB port. Hopefully this should make accessing our product easier.

I am sure you are right - in the future (5-10 years) the new industrial equipment will not even require serial connections - probably Ethernet and/or USB.

But that doesn't help NOW. We have 2000 PLC's in our plant. They work fine, and we will probably still have them 5 or even 10 years from now. Only about 5% currently have Ethernet connectivity -- but guess what!! You need a serial connection to configure the Ethernet connection!

In addition to PLC's we have motion control boards, message displays, small HMI's, light curtains, bar code printers all requiring serial connections to operate AND to program/configure.

So the problem is going to be with us for quite a while, whether we like it or not.

 

[Mickey]

2000 !!! PLC's in one plant? WOW

 

[Foghorn22]

Not all RS-232 drivers are created equal

I have done some additional research that relates to what you are saying here. It has to do with voltage and power levels in RS-232 drivers (this applies to built-in as well as USB).

The official RS-232 standard says that the output signal level would be:

• Logical "1" = -3v to -25 v
• Logical "0" = +3v to +25 v

This gives +/- 3 volts for noise.

I found out there are 3 different "categories" of serial port drivers used on computers, based on the voltage level of the computer itself:

1. Drivers which require plus (+) and minus (-) voltage power supplies such as the 1488 series of interface integrated circuits. (Most desktop and tower PCs use this type of driver.)
2. Low power drivers which require one +5 volt power supply. This type of driver has an internal charge pump for voltage conversion. (Many industrial microprocessor controls use this type of driver.)
3. Low voltage (3.3 v) and low power drivers which meet the EIA-562 Standard. (Used on notebooks and laptops.)

The problem that leaps out at me is that we no longer can count on getting the large voltage swings that we are accustomed to. It is quite possible that our PLC's and other industrial devices don't really expect to see a mere +/- 3.5 volt swing, especially in the presence of a lot of industrial noise.

The charge pump design uses capacitive voltage doublers (an old trick from the tube days) to generate +/- 6.6 volts from the 3.3 volt supply. But these circuits have very low power capabilities. If the device loads down the line much, these voltages can drop considerably. See links for more detail:
http://www.analog.com/UploadedFiles/Data_Sheets/79657292ADM3202_22_1385_b.pdf


http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1007,C1016,D4268


Seems to me we are at the mercy of the RS-232 driver built into our mother board or USB converter. Yes, they may "technically" meet the RS-232 spec (or the even lower-voltage RS-562), but it looks like they may be on the 'ragged edge' of actually functioning.

Has anyone ever measured the actual voltage swing they get on serial links from various kinds of PC's, laptops, USB and PCMCIA converters? Might be interesting. And I also wonder if this could actually change depending on whether a laptop was plugged in or on battery power??