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.

Anyways, 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.