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I was tasked to do a serial port related software and I'm trying to do some initial preparations. I'm using windows 7.

  1. My laptop physically only has USB ports (besides the screen), is it possible to check serial ports like this at all? Will any cable adapters help?

  2. Windows 7 device manager shows nothing is connected to serial ports, which makes sense. However I've written a small application (in node.js) to list the connected serial ports. It lists COM3 as a connected port (though no information on manufacturer or any id). Is there an explanation to this?

Yaron Naveh
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  • *"My laptop physically only has USB **adapters**"* -- Don't you mean that it has USB **ports**? An adapter would plug into the port. The adapter would also have a specific function, such as provide a RS-232 port, or provide a VGA port, or provide audio conversion, or provide TV tuner capability etc. – sawdust May 26 '14 at 00:42

1 Answers1

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To software, a USB-to-RS232 adapter is no different than any other RS232 serial port. It will show up on COM1 or whatever just like a physical port would.

If you have a serial port showing up on your system on COM3, then something is there. It isn't uncommon for RS232 ports to be on the motherboard, but not be exposed externally. Also, if your laptop has a dial-up modem, then this would be on the COM port as well. If you have a cellular radio, these are often on COM ports.

Brad
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  • thanks, I don't have any serial port outlet in my laptop (physically), it's all just USB . Is there still a way to connect something such that in device manager I see some COM connected? or will my PC treat everything as USB. – Yaron Naveh May 24 '14 at 23:05
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    @YaronNaveh USB ports and traditional serial ports (usually RS-232) aren't anything at all alike. Think of USB like an external PCI bus. There is a whole protocol in place which devices use to identify themselves and communicate with services on the host. RS-232 serial ports and similar have no intrinsic protocol. You send and receive bytes. There are modes of operation, sure, but nothing that automatically establishes a communication link beyond the physical layer. Like I said, that COM port you see could be on your motherboard, but you can't very well connect something without a port. – Brad May 24 '14 at 23:13
  • @YaronNaveh Get a USB-to-serial adapter. They cost $2 online. – Brad May 24 '14 at 23:14
  • Thanks! So if I use the USB-to-serial adapter, will my pc (e.g. in device manager) identify it as a PORT (COM/LPT) and assign a COM number to it (e.g. COM4)? Does it make sense that I have no physical serial entry in my box? – Yaron Naveh May 24 '14 at 23:17
  • Yes, exactly, and yes it makes sense. I have 3 of these things hanging off my laptop right now. (1 RS-485 depth sounder, 1 GPS unit, and 1 GPRS modem) – Brad May 24 '14 at 23:21