Serial port "sort of" problem

Discussion in 'Windows 7 Help and Support' started by Kurtwm, Feb 16, 2014.

  1. Kurtwm

    Kurtwm New Member

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    Not sure if this thread belongs here or in networks.

    I have a point of sales system that is Windows 7 based. Connected to serial port 3 is a customer pole display that shows the total for each item sold.

    My problem is that my point of sale software say that it cannot connect the pole display to the serial port. To fix this I have to go into device manger and uninstall the com port and then reboot and restart the POS software. I am unable to figure out why that is. I was thinking that something else is grabbing the com port but there is nothing else running besides the POS software.

    Not sure if I provided enough details to explain my problem. I would really appreciate it if someone can help me out. Thanks
     
  2. Fixer1234

    Fixer1234 Senior Member

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    Some questions if this has not already been overtaken by events:
    How many physical serial ports does the computer have in all?
    Are they all incorporated into the computer case or are you using some form of add-on port expander?
    If you are using a port expander, what serial ports are included on the computer case, what serial ports are on the expander, and how does the expander connect to your computer?
    How many serial devices are connected to the computer?
    Are serial ports 1 and 2 connected to devices? If so, does the device on serial port 1 work correctly?
    Is there a serial port 4 and is it connected to a device and if so, do devices on both ports 2 and 4 work correctly?
    What kind of device is connected to each serial port (what function does it perform)?
    When you use the term "point of sale" to describe devices connected via the serial ports, are these "dumb" devices (simple peripherals or accessories that perform a single function that requires the processing power of the main computer and what is sent over the serial connection is essentially "raw" data), or are they essentially computers that can perform their function independently and the serial port just provides a communication link for "high level" information? Do the POS devices have their own operating system and software and get booted up on their own to operate?
     
  3. Fixer1234

    Fixer1234 Senior Member

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    One more question: what is the approximate length of each serial cable connected to the computer (but particularly on port 3)?
     
  4. Kurtwm

    Kurtwm New Member

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    Thank you for your response. Yes, I still have not resolved this problem.
    There are 5 serial ports (besides 5 USB ports). They are all incorporated into the computer. No expander is used.

    Two serial ports are being used. One for the customer display (listing each item sold) and the other is used by a barcode scanner. Both ports work just fine and I never have a problem with the barcode scanner port. If for any reason the system reboots the serial port 3 comes up as being used by "something else". That's when I go through the ritual of uninstalling port 3 and rebooting the system. Then it connect fine and works ok until the next time. Lucky it does not happen very often.
    The operating system is Windows 7 Professional.

    The barcode scanner is a dumb device sending the scanned code to the port where it is picked up by the point of sales software. The custom pole display is sort of a dumb device but it is programmable to display the data send and displayed in a format that I want it to be in. I.e. description of the item sold, price of item and the total sold, in my case. The pole display does have a print driver loaded on the windows system. In my case it is a generic Windows print driver. The pos software passes the data to the driver and it passes it on to the display.

    All cables are no longer than 4 feet, the pole display cable only 12 inches.

    Hope this makes sense and I answered your questions.

    I read somewhere that perhaps a change in the register is needed, but I am hesitant to make register changes unless I fairly confident it works.
     
  5. Fixer1234

    Fixer1234 Senior Member

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    These kinds of problems used to be common back in the ancient days when serial ports were used. They were solved with the introduction of plug-and-play and USB ports. It is hard to find a computer today that comes with serial ports, especially more than one. You are lucky that you only have two serial devices connected because conflicts get common when you exceed that. If you need to expand your system, look for devices that will connect through a different type of port, preferably USB.

    Your problem is probably related either to a port conflict or the device or driver.

    Each serial port is defined by the combination of a memory address and what is called an interrupt request (IRQ) number. There are default values for these, which can be modified if necessary, and it may have been necessary in order to go to five ports. Normally, ports 1 and 3 share the same IRQ, as do ports 2 and 4. That sharing was often the cause of conflicts. The port settings are typically changed either via jumpers on the serial interface inside the computer or through BIOS settings or software. Improper settings can cause conflicts. Some systems have the ability to "discover" the serial ports, which could appear as the ports not being recognized one time, but working another.

    There are a few things to look at and try that may fix the problem without your having to do anything technical:
    1. Make sure that your two devices are not sharing an IRQ (don't plug them into the combination of ports 1 and 3 or 2 and 4).
    2. Try plugging the display into a serial port other than 3 (there could be a problem with one port but not others). So try using port combination 1 and 2 for the two devices. If you still have a problem, move both devices to ports 3 and 4.
    3. Try swapping ports for the two devices. Plug the display into a port that you know works for the scanner.
    If the scanner works on every port and the display does not work on any port (by "not work", I mean produces the problem you are experiencing), the problem is not with the serial ports. In that case, my bet would be on the print driver. In the days of serial printers, that was a common problem, particularly if port settings other than the default were used. See if you can get a driver from the display manufacturer (might be available online).

    If none of those suggestions solves the problem, come back for round 2. BTW, I'm not aware of anything you could manually change in the registry that would solve the problem.
     
  6. Fixer1234

    Fixer1234 Senior Member

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    A couple of quick additions:

    • When you move the devices to different ports, you will need to change some settings somewhere to tell the computer and software where to find them.
    • If the original installation did not go perfectly and you did any kind of re-install or previously moved things around, you could have phantom or virtual devices left over that could be causing the problem (the computer would think they are real and conflicting).
     

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