Although serial port is considered as 'legacy technology' sometimes some strange persons needs to use it. Of course, on our Macs with USB ports only it's still possible hovever it's not painless.
What do you need?
1. First of all - USB->Serial adapter with popular chipset PL2303.
2. Next - you need a drivers: PL2303.
3. A software. It's quite obvious to start screen using following command: