The Serial Bus (RS-485)The Serial Bus is nothing but a panel with 15 DB9 connectors wired in parallel. One of those connects to the Master Linux hosts; the others, to PI units.
It is highly recommended to use a networked Device Server equipment instead of connecting the BUS to computer physical serial ports (via RS485/422-to-RS232 adapter, of course). There are several advantages on doing that:
* Facilitates future expansion of the topology.
* Removes the need for (not always reliable) RS485/422-to-RS232 adapters.
* Allows the Master Linux host to be virtual. This is specially interesting if you opt for an automatic-fail-over arrangement using two hosts.
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