[Elecraft] K3: COM1 and COM3 question

[Don Wilhelm]

Jim,

Let me try an explanation as simple as I can put it.

The COM port numbers are set at the computer end.  First the OS assigns 
port numbers to the physical COM ports that are present on that computer.

You connect a cable and a terminal device (the K3 or P3 or several of 
them) each to a physical port on that computer - you have to know which 
connector on the computer corresponds to COM1 through COM nnn - normally 
a computer with one true serial port will have COM1 on that connector - 
for those with multiple true serial ports, you have to know which number 
corresponds with each port - that information is normally silkscreened 
on the motherboard.  For add-on cards, consult the card instructions.
With USB adapters, you can usually find the relationship in Device 
Manager - the numbers are usually higher.  If you don't know which 
adapter is which, unplug it and see which port numbers go away, then 
plug it back in and see which numbers appear.

After you know which port numbers are assigned to which serial 
connector, then you can go to the software application and tell it to 
talk to a particular device over a particular COM port (the one you have 
cabled to your device).  Some applications will scan through the 
available ports to try to find what it thinks is a valid open port with 
the desired device connected (and powered on) at the other end of the 
cable.  The software application will seize the port and makes it busy 
to all other applications.  The operating system passes whatever flows 
on that port over to the application.

The terminal device does not know which computer port it is connected to 
- it sees data coming in over the TXD signal line and responds on the 
RXD signal line - the computer and application sorts out which device it 
is talking to.

73,
Don W3FPR

On 11/2/2011 6:25 PM, Jim Dunstan wrote:
> At 05:38 PM 11/2/2011 -0400, you wrote:
>> Jim,
>>
>> Sorry to disagree, but there is no way to set the COM Port on either the
>> K3 nor the P3.
>> Setting the baud rate - yes, but the computer (or the computer
>> application software) determines which COM port is to be assigned to a
>> particular connector or cable.
>>
>> 73,
>> Don W3FPR
> I am sure you are correct.  I don't own a K3.  But the original post
> mentioned two K3 operating positions each
> controlled by separate computers.  One computer uses Com1 on the RS232 port
> and the other uses Com3.
>
> There was no question ... but a request for an explanation.
>
> Perhaps you can provide the explanation.
>
> Thanks
>
> Jim, VE3CI
>
>
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