Serial ports really availoable?

Discussion in 'General Electronics Chat' started by atferrari, Jan 30, 2006.

  1. atferrari

    Thread Starter AAC Fanatic!

    Jan 6, 2004
    My laptop, no surprise, has no connectors for serial ports.

    The BIOS details, show:

    COM1 in 3F8 with IRQ 4
    COM2 in 2F8 with IRQ 3

    The "system information" utility shows

    COM1 in 3F8 -3FF with IRQ 4
    COM4 with no address nor IRQ

    MY questions:

    Is all this a leftover that nobody care to eliminate?
    What's the reason for such inconsistent info?
    Which is true?
    How to know the above? (How to test?)

    If I open my laptop, could I identify a valid point where to take the signal for a serial port if I accept the risk to install a proper connector?

    All this is quite puzzling for me. Help appreciated.
  2. chesart1

    Senior Member

    Jan 23, 2006

    Have you visited the site of the laptop manufacturer to search for information on serial ports for your laptop?

  3. Gadget

    Distinguished Member

    Jan 10, 2006
    Perhaps the working COM1 port is connected to an internal Modem..??
    If there are no 9 pin com port sockets on the rear, then obviously there are no external com ports.
    If you need a Com port, I suggest one of the many cheap and readily available USB to COM port adaptors.
  4. n9352527

    AAC Fanatic!

    Oct 14, 2005
    The most likely explanation is that the chip that provides the serial port function is there inside. This I/O chip is usually used for many purposes, not only for serial port. This is why it can't be eliminated completely even when there is no serial port connector provided. The BIOS and the OS (which reads the system info from the BIOS) still have to initialise and control all the I/O chip functions and this is why the serial port is still listed as available (and taking valuable resources!).

    You could always open the laptop and find out where the connections for the serial port are, but depending on the chip design it might be necessary to provide a physical driver chip. Some I/O chip only outputs logic compatible signals and it is up to the designer to convert that into the appropriate RS232 signal levels. Having said that, it is probably safer and cheaper (in case you break something up!) to get an external serial port or converter to serial port (USB to serial, ethernet to serial, etc).
  5. chesart1

    Senior Member

    Jan 23, 2006

    The information is not inconsistent, though it is confusing. Generally, four addresses are associated with each COM port. Typically the specifications will only list the lowest address associated with each COM port. The COM port addresses are used by the software for configuration purposes.

    Your COM port is basically a serial port dedicated for a specific purpose. An easy way to test a COM port is to configure an external device for that COM port and test the functionality of the device.

    Hopefully, your laptop diagnostics include COM port testing.

    More thorough testing involves creating a loop back cable so you can send data out and receive it. Most hardware also allows internal loop back testing which does not require an external cable. However, this type of testing requires you to design the software to transmit, receive and compare the data sent to the data received.