What does button on PIC programming cable do?

I have 4 PIC programming cables. One works fine, the other 3 will not let the robotc software see the PIC controller. I get the message “failed to communicate with the robot on com port 5” . If I just change to the good PIC programming cable it works fine. I am wondering if the button on the box in mid-cable is an off / on switch but even pressing it does not seem to make a difference. Thanks for any advice.

After a quick search, I found this thread that answers half of your question.

The cable is most likely broken, it happens - our club has a few that are.

I guess I have some bad cables. I can’t imagine what makes the cables go bad but that makes sense.

It may also be a driver issue. Prolific updated the driver to try and stop the use of “pirated” cables, unfortunately this has caused some cables that are probably legitimate to stop working. I posted a link somewhere with the results of various cable/driver combinations that I tested, I will dig that out later and append to this post.

Edit

Ok, so here’s the link. This testing was for Windows XP (which I realize is mostly obsolete now) but the information and explanation behind it is still valid. I will check what is going on with ROBOTC 3.62 and perhaps the 4.03 beta at some point and update the information. I will probably concentrate on Win 7 with the revised testing.

https://vexforum.com/showpost.php?p=318408&postcount=15

Edit2:

Updated information for Windows 7 here.
https://vexforum.com/t/prolific-serial-drivers-and-bad-cables/24681/1