How does an EIDE drive become removable?

I am trying to set up an Ampro P5v system as a compact flash card
programmer, so I would like to be able to program a card, remove it, and
plug in another without rebooting the machine. The cards themselves can
take this kind of treatment, but QNX and/or the computer cannot. The
system seems to lose track of the entire file system (can no longer find
“ls,” for example) after I remove the target card. If I unmount the
target card first, I can pull it out without affecting the system, but
things fall apart when I plug a card back in, even if I don’t try to
mount the card. I know that Fsys.eide can handle removable drives, and
I was wondering how the system figures out whether or not a drive is
removable. Is there any way that I can tell Fsys and Fsys.eide to treat
the target CF card as a removable drive?