The usual way of checking a cable is with a multimeter,
available for $10 or so at numerous stores. You can check the whole
shebang by connecting com1 on computer 1 to com1 on computer 2,
then run kermit or some similar program, and watch yourself
type on computer 1 with the screen on computer 2 and vice
The above is just an example, there are more elaborate
things you can do if you are running Linux or something similar.
Speaking only for myself,
> > Hello,
> > Is there a shareware or freeware software to check serial ports in a
> > Windows 98 based PC ? if so please where can I download it ? what is it
> > call this software ?
> Best test for a serial port is an actual modem. Most of the software
> requires a loopback device connected to the port to thoroughly check it.
> Here's a link to a search I did at Cnet...
> > What about a dos command line ? what is the command to test the COM
> > ports ?
> There are DOS programs that do the testing, again with the same requirements
> The reason for the external loopback tool is because the software doesn't
> test all the way out without one, it just creates a loopback within the UART
> > What about checking a null modem cable ( pin 2 with 3, 3 with 2 and 5
> > with 5 ) how can I check if a cable is properly wired ?
> Sure, easiest test is to put the cable between two computers. But you want
> to do more than the wiring you've shown above. I don't have the wiring info
> handy though. It's cheap and easier to buy a Null modem adapter than to wire
> a cable yourself.
> > Possible to connected in the same PC between com1 and com2 and check it
> > ? How ? any software or command line to execute ? what is this DOS
> > command ?
> I used to do that back in the old days (pre-5.0 version of DOS) using a
> multitasker called Desqview.
> I haven't tried it with Win9x but it's worth a try. Open two copies of a
> terminal program (preferably a DOS one, not a Windows type), put one on 1
> port and the other on another port and see if you can type to each.