On Thu, 2008-03-27 at 23:32 -0400, Joachim Thiemann wrote:
[HHC ROMs]
How difficult would it be to copy a ROM? The
bank ROMs are simply
EPROMs with sticky paper labels, I think I could simply erase one and
the reprogram it with a homebuild adapter so as not to damage the
carrier...
If it's just an ordinary ROM, extremely easy. You just read it, and
blow another.
THey are stnadard EPROMs, in that they're not custom chips, but they're
nto a particlarly common type. I forget the part number, but they're an
8K*8 chip in a 24 pin DIL package (24 pins = 2 power + 8 data + 13
address + CS/). Not all programmers can handle them.
In the HHC, they're fitted into little plastic carriers which then plug
into the sockets on the main board. IIRC, they go in 'upside down' --
that is the top face of the package -- the face where the window is --
ends up facing the board. One thing to watch for.
The other curiousity is that in the HHC, the CS/ pin is tied to the A13
line. ROM chip select is done by switching the power to the ICs (the 3
ROM sockets are bank=switched into the same bit of the CPU address
space). I am told that at least one ROM for the HHC was a 16K one, of
course in a 24 pin package but with no CS/ line. I don;t think that was a
stnadard chip, though.
Oh, and the A12 lins is inverted between the CPU and the ROM socket, just
to confuse you if you're creating a ROM image.
-tony