Figure out which of the following scenarios applies to you, and attach your USB-to-serial adapter(s) according to the options you see.
If you are using a Raspberry Pi with four USB ports, then use the pair of USB ports next to the Ethernet port, not the ones in the corner.
If you are using a Raspberry Pi model A or A+, consider its one USB port to be the “lower” port in the instructions below. If you have a USB hub attached to it, then port 2 on that hub is the “upper” port, and port 3 on that hub is the “lower” port. Since the physical ports these correspond to may vary by hub, you may need to try different ports to figure out which is which.
You’ll see mentioned below the “lowest-numbered” or “highest-numbered” port in a USB hub, which isn’t necessarily obvious. If you have a USB hub, try the leftmost or topmost port, and if that doesn’t work, try the rightmost or bottommost port. If you want to definitively know, see the note at the end.
If you have an Apple IIe with a single Super Serial Card, then “modem port” in these instructions refers to that card, and “printer port” is unavailable. If you have two Super Serial Cards, then the order is the reverse of what you might expect; “modem port” refers to slot 1, while “printer port” refers to slot 2. (Thanks to David Laffineuse for this report.)
You have one USB-to-serial adapter, and want to use it for virtual drives
You can use:
- the lower USB port
- any port in a hub on the lower USB port if it is the only USB-to-serial adapter in the hub
- the lowest-numbered port on a hub with multiple USB-to-serial adapters
Connect the adapter to a serial cable attached to to your Apple II modem port.
You have one USB-to-serial adapter, and want to use it for internet
You can use:
- the upper USB port
- any port in a hub on the upper USB port if it is the only USB-to-serial adapter in the hub
- the highest-numbered port on a hub with multiple USB-to-serial adapters
Connect the adapter to a serial cable attached to to your Apple II printer port.
You have two USB-to-serial adapters
Do both of the above.
How to figure out the lowest or highest numbered port on your USB hub
You can attach two USB-to-serial adapters to a USB hub attached to either USB port on the Pi. A2CLOUD tells them apart based on their being attached to a lower numbered port for virtual drives, and a higher numbered port for internet.
I did it this way so you can simply try the ports at either end of the USB hub and see if you get the results you expect. But If you want to know the actual port number, detach all of your USB-to-serial adapters, then plug in one adapter. Then type
ls /dev/ttyUSBlower_hub* and see what it shows you. The number at the end is your USB port number. You can then move the adapter to a different port and repeat until you figure out which one is the lowest and which one is the highest.