"MIG" wrote in message
...
On Jul 16, 4:22 pm, Roland Perry wrote:
In message
, at
05:47:38 on Wed, 16 Jul 2008, remarked:

From wikipedia:

"A control store is the part of a CPU's control unit that stores the
CPU's microprogram"

"A control store is usually implemented as a diode-array of read-only
memory"

I'm a fan of Wikipedia, but that stuff is just gibberish.

So I guess at that level you could put forward a valid argument for it
being hard wired diodes, or software in the sense of the way the
diodes are wired. Or both! But then again I suppose you could say the
same about any read only ROM.

There any many technologies that can be used to implement a ROM,
including the presence and absence of diodes in a matrix, and even the
ability to erase or restore such diodes in the field. This is
ludicrously technology-specific, however, and who is to say what a
generic CPU uses to store its microcode. (If you had asked me yesterday,
I might have said "the presence of absence of conductors between logic
gates").

This all might as well be a foreign language to me, but ... does one
or other hypothesis explain why a card can be permanently disabled by
being touched on a pad rather than being able to be reset?

-------------------------------------------------------------------------

Nope. There is no reason why touching your card on an incompatible pad
would render the card unusable, unless the software was written to do this
(by accident or design) in the same way as say entering your bank (or mobile
phone) PIN in incorrectly.

Issuing such cards with no way to reset them by software would be remiss of
the designers.

My guess is that the reset requires the card to be attached to special
hardware and they decided that collecting all the cards and doing this
centrally was easer than doing it at every Underground station.

tim