You can connect N RS232 devices together in a ring topology, if the software supports it.

Basically:
Each message has the form of <dest><src><payload>

You send your message to a recipient, and mark yourself as the source.
You pass on any messages that aren't for you.
You receive any messages that are for you.

You swallow any messages you sent.
They've gone around the ring once. You might need to do something else as the recipient is apparently asleep or gone or ?

For bonus points, configure the hub so that unplugged devices are bypassed automatically (relay on CTS?)

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