Clearly /dev/ttyS1 is not OK, but I've no idea how to
set it up so it is OK - I'd be grateful for any help.
Sounds like the FC7 kernel was built with a very low number of serial
ports defined so it filled in /dev/ttyS1 with the motherboard port entry
(not present it seems), then filled 2, 3 and filled 0 back in as a last
desperate act as it couldn't fill 4,5,6...