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Elan Digital Systems Ltd. 6 CF232 USER’S GUIDE
4. CF232 REGISTER INTERFACE
Full details of the CF232’s register interface can be found in the
VPU16550 data sheet, available at Elan’s website
http://www.pccard.co.uk
For reference, the CF232 and the CF232-5 both behave as a 5V card
to the host system because Vs1 and Vs2 pins are no connects. This
is to make the host default to 5V when possible, giving the highest
RS232 output signals and therefore best noise margins. The Card
Information Structure does not define any 3.3V tuples because some
platforms will also take this as a sign to run at 3.3V even when 5V is
available. On a PDA or HPC, the host will power the card at 5V if
it’s available, or 3.3V otherwise (despite there being no 3.3V tuple
entries).