This adapter is a plug-in replacement for the 5114, 5514 and 6514 CMOS SRAM chips used in early Williams video arcade games. It is intended to eliminate the problem of intermittent settings and high score loss or corruption that often occurs when using a switched mode power supply ("switcher") instead of the original linear power supply in games such as Robotron, Sinistar, Joust, Stargate, Bubbles, Blaster and Splat. (Sorry, Defender is not supported)
An ST M48Z02 internal battery backed SRAM chip which write-protects itself when the power supply drops below 4.75V, so it's unaffected by the CPU writing out garbage during power off. According to the datasheet, the internal lithium battery should retain the memory for > 10 years. It also eliminates the need to use the original AA battery holder (or lithium coin cell) on the game PCB.
To install it, just replace the original CMOS chip (e.g. 5114, 5514, 6514) with the included DIP socket and plug the adapter in to the socket.
The 2-pin header is for a jumper which can be used to switch between the lower and upper bank of memory, so two sets of high scores and settings can be stored and accessed on the same chip. For example, install the jumper and set the game for "tournament" settings; remove the jumper and set the game for "marathon" settings – you can then use the jumper (or wire up a toggle switch) to easily switch between the two modes and the high scores associated with each.
The 4 extra pads on the adapter are routed to data bits D4-D7 of the NVRAM, so this adapter could be used on a Bubbles board if you wire these pads to the corresponding data pins of the second CMOS RAM socket on the game PCB.
These also have been confirmed to work in Stern Frenzy and Berzerk ZPU boards. Just replace the CMOS RAM chip at location 1E with the NVRAM adapter and set the W11 jumper for a "6514" chip as indicated in the manual. (thanks to KLOV member KI4SWY for testing this!)