I have built a couple multi-panels in the past. I wonder if instead of each having a separate usb cable connected to the same computer, they could share the same usb/serial cable?

What I did is connect each multi-panel to a different com port and a different rss feed. but this has taken all my usb ports so I am thinking if it could be possible to have another mcu with a single TX/RX usb read the feed and this mcu send specific info via SPI pins to each multipanel's master mcu RX pin.

OR connect all masters TX/RX pins together sharing a single usb

OR what would be the best way to accomplish this?

Any help and suggestions is really appreciated.

the idea is that each multi-panel should display different text sharing the same usb cable

I am not sure if this is possible and if it is what would be the best approach?

Yes it is possible. I2C and SPI are both master/slave communication methods built-in to your ATmega that would work but I2c is probably a little harder to get working. That said, the easiest and quickest solution may be to get a USB hub and keep going with your current method.

Look at the Master/Slave SPI and Master/Slave I2C threads for an example of each and see if you want to pursue one of these methods. There's also some articles on I2c in the code library.

The best approach would be to get the Master/Slave SPI examples working as they are and then incorporate them into your project. Probably one ATmega reading all the rss feeds and then passing the information to the appropriate slave would be a good approach.