Tengen Lockout Chips
The original chip
RAMBO-1 which includes the lockout function
How it works:
This is a direct clone of Nintendo's own chip. Tengen used some dirty tricks to snag the source code
to nintendo's own chip from the US Copyright Office. There's alot of stuff on the 'net about
this whole sordid tale so I won't reproduce it here. Do a google search or similar.
Tengen called this their "Rabbit" chip for some reason. It appears to be an exact clone of
the Nintendo chip, down to the pinout and connections. The RAMBO-1 integrates the functionality
of the chip into the mapper, to reduce costs and board space. Kinda clever.