I thought if there are no ide/ata units attached if it's possible to hook up a
TTL output to one of the data pins directly to sample with software a la
inw(0x1F0) without blowing up something.. ?
Are you sure you're not thinking of the parallel printer port?
Before all the UDMA stuff, cheap IDE cards used to connect the data lines
of the IDE cable directly to the data lines of the ISA bus through 330-ohm
resistors.
If you look at one of the more recent ATA specifications (draft versions
should be available on the net) there's a table of what types of drivers
are to be used on each pin. The data lines are all tristate, some of the
other lines can be totem-pole or open-collector. And some of them have
pullup resistors, while others have pulldowns. What a mess.
-- uns