Post by Ashton CrusherOn Mon, 26 Oct 2009 21:37:57 -0700, bllsht
Post by bllshtPost by WesleyIs the transponder (key) programmed for the vehicle, or is the vehicle
programmed to recognize the transponder? It would seem to me that the car
would be more easily reprogrammed than the "key"... Not that the system
designers would necessarily think the same way I do of course...!
Wesley
Both are true. The key is programmed with info from the vehicle, and
the vehicle is programmed with the key's ID.
The key's ID can be erased from the vehicle, but once programmed, the
key cannot be reprogrammed to another vehicle.
What would be the point? I fail to see the logic of it. I'm not
saying you are wrong.
I don't know the technology used in those keys, but there are lots of
write-once memory technologies: they come from the foundry with all the
bits set to 1 (or 0); you can write any bit you want to the other state,
but once written you can't change it back. So you can set a code by
setting a bunch of 1's, and you can wipe the code by setting all the
other 1's. But you can't set a new code.
The clearest example is the original PROM (which is completely obsolete,
but still a good example): comes programmed with all 0's. You set a 1
by putting a big enough current through a junction to quite literally
blow a tiny fuse. Once you've done that you can't set it back to a 0.
--
As we enjoy great advantages from the inventions of others, we should
be glad of an opportunity to serve others by any invention of ours;
and this we should do freely and generously. (Benjamin Franklin)