Transfer cas files to atari 800XL with PL2303TA adapter and this software.
Your must have a usb to uart adapter how this here or similar. The best is with PL2303 chip.
Here is the pinout from the atari sio connector.
| PL2303 | Atari SIO |
|---|---|
| TX | Pin 3 |
| GND | Pin 4 |