
There were a few designs.  You should be concerned with BC5 and BC6.  BC6 is
much more reliable, Nintendo caught on to our BC5 circuit and tried to
protect against it, so we invented BC6 and they gave up.  I think they
decided it was better to let us stay in business, so that they could say the
weren't involved in anti-trust activities.
 
A 74LS377 was used to control both the memory
paging, and the protection lockout circuit.  The other large IC that isn't a
rom was a 4051 in the earlier version, and later it was a 7660 voltage
doubler.
 
The first protection circuit sent a pulse of 10 or so volts into the
nintendo copy chip, to lock it up.  The second actually generated -5 volts,
and sent that, because Nintendo put a clamp to prevent voltages over the
limit, so we had to take advantage of their forgetting to protect against
negative voltages.   Their protection chip was a little 4004 microcontroller
that expected to be sent a checksum sequence.  We couldn't send the checksum
like it wanted because that violated their patent, so we turned it off
instead.  It gets zapped and locks up with the game still enabled.  Perhaps
one out of 100,000 units will actually be permanently disabled,  which might
be considered "damaged", but it was so low in rate that it's difficult to
say if the circuit caused it, or if insertion of cartridges and static
electricity caused it.  It just meant the protection chip stopped working
altogether.  No one complained much about it, because they could still use
their units.  I think we fixed one or two for people.  We have a
modification that completely removes the circuit, I can fax you that too.
 
The other patent you have to be aware of is the cartridge shape.  It's a
violation of their patent to have the bevels on the corners, they actually
tricked the patent office into believing that putting bevels to prevent
upside down insertion was an "invention".   So we made our cartridges flat,
and skinnier than the nintendo cartridges, so that they didn't have any
bevel, but would still fit only one way.  If you want to make new games with
relative safety, you would have to use that cartridge shape also.  You're
welcome to that too, it was my invention.
 
We have some primitive drawing tools, which some of the web pages interested
in old nintendos might be able to give you.  The program was called
"nindraw", and was a way to draw tile oriented graphics with the limited
color palettes of the nintendo.  Each set of level graphics was fit into an
8K range, 4K switchable.  It supported multiple 8K ranges, controlled by the
377 latch.  The program memory was probably banked as 32K, and you could
have multiple banks by sharing the latches in the same way.
 
2 bits of the 377 were used to control the protection circuit, the other 6
were used for program and video banking, allowing 8 banks of each.
