What is a COM port used for?

[Bob-1996]

What is the purpose of a COM port, its function and speed? I can't seem to find any helpful sources of information on the internet. All answers will be GREATLY appreciated. Thanks in advance!

 

[_Pete_]

A COM port is just a communications port. Essentially it is any of the sockets or plugs on a computer or digital device that allow you to plug in a device or peripheral that the computer/digital device can "COMMUNICATE" with ie pass information to and get information from. Most people, though, will recognise COM port as being the serial port on older computers. Some older networking cards and modems used this port to connect to a computer. Modems and network cards are devices that allow the computer to COMMUNICATE, hence COM, with the outside world or other computers and devices. Most ccomputers these days do not come with a serial or COM port as data transfer via a serial port was relatively slow compared to modern USB three or even wireless and bluetooth, bluetooth being essentially a wireless connection.

 

[Agent Smith]

Back in the day serial port adapters were used for devices like Palm Pilot syncing, printers, etc. Now USB is the standard. A COM port now a days is mostly used for the computer hobbyist for certain things. One application is for a data slicer used to decode pager traffic. Yeah, pagers. Doctors use them still in this day and age. But with SDR (Software Defined Radio), you don't need a data slicer.

My old police scanner connected to the COM port of my computer so that I could control and program it. There are also COM port to USB adapters, but depending on your application, they may not work.

I have actually sent COM port data over the network. So I was able to control my scanner from a laptop on a WIFI connection. Serproxy is one of the applications I used. Great little peace of software. Now a days you can just run Teamviewer and remote into the computer with another computer or even a smartphone. Audio can be streamed with Teamspeak or Icecast.

 

[Geoff]

As others have said, it was popular before USB was widespread in the use of programming external peripherals, PDAs, etc. Today it's not used much, but many still rely on legacy gear that uses COM ports since unlike USB, you don't need drivers to get devices to communicate properly like you do with USB. You just select the COM port and speed in the software. Actually, there are quite a few devices that have a USB port but are actually COM-based devices that simply have an integrated serial to USB adapter.

 

[strollin]

Back in the early days of PCs, there were only 2 types of ports, serial and parallel. The parallel port (LPT) was used almost exclusively for printers while the serial port (COM) was used for everything else. Mice and modems were the main uses for serial ports but there were other devices that used serial ports as well (my first GPS attached via the serial port).

The port had to be configured to match the speed of the device that was attached to it. Some of the parameters were the baud rate (speed, typically 9600 but could be 1200 to 115000), number of bits, (usually 7 or 8), whether to use parity or not, stop bits, etc...

There are adapters that let you attach serial port devices to a USB port, the USB port can then be configured as a COM port. Look in Device Manager for a COM port such as COM1. If you find it, right-click and go into properties. There is a Port Settings tab that lets you set the various parameters for the port.

You should be able to get lots of info by doing a search on COM or serial port in google or your favorite search engine.

 

[tremmor]

Funny it was brought up. Havent used at home in 20 yrs i think.
Still used in industry for PLC's and logic controls for industry.
Thats it that i know of. Has to be a real serial port. usb to serial would never work.

 

[voyagerfan99]

Has to be a real serial port. usb to serial would never work.

Not true. In networking we use USB-->Console ports for connecting to managed network switches, and they communicate over COM ports (virtual, of course, but still use the COM protocols and speeds).

 

[Geoff]

Funny it was brought up. Havent used at home in 20 yrs i think.
Still used in industry for PLC's and logic controls for industry.
Thats it that i know of. Has to be a real serial port. usb to serial would never work.

That's funny that you haven't used it in 20 years, I've used the serial port (granted USB to serial since my PC doesn't have a COM port) several times this year alone. Most of it is for my amateur radio hobbies which still use serial-based programming.

While USB to serial adapters are picky, they do work.

 

[tremmor]

im saying a lot of industrial devices would not work. requires a true port card.
I have a Black card if needed for programming. usb to com would never ever work.
Dell computers is the only one that may have a serial port card built in.
At least was.

 

[Geoff]

im saying a lot of industrial devices would not work. requires a true port card.
I have a Black card if needed for programming. usb to com would never ever work.
Dell computers is the only one that may have a serial port card built in.
At least was.

Perhaps it requires a null modem adapter. Lots of peripherals don't work with a direct serial to USB-to-serial adapter without one.

 

[beers]

While USB to serial adapters are picky, they do work.

I've found a lot of the time the application may not handle the USB driver correctly, causing hangs.

I have been getting that with Putty a lot since a certain patch in the last few years on Prolific adapters. Using Tera Term doesn't exhibit the same behavior though.

There isn't a reason that an adapter shouldn't work if the device is utilizing RS232.

 

[TrainTrackHack]

Serial ports are still often used for kernel debugging on physical hardware, especially for very low-level stuff when you want to initialise as few devices as possible. I think it's because of the simplicity of it and the fact that you can do that very early on in the boot process with minimal drivers (so you can communicate with the machine even before the USB subsystem, networking or any other hardware is initialised/their drivers loaded). At least in the case of Linux and ReactOS the COM ports on the target machine do have to be "real" (not usb-serial).