At u5 (BUF1) = DS1216 -
8702
This is a very interesting "module" from Dallas Semiconductor. To quote
the data sheet, which can be found here
http://www.ortodoxism.ro/datasheets/maxim/DS1216-DS1216D.pdf:
"The DS1216 SmartWatch RAM and SmartWatch ROM Sockets are 600mil-wide
DIP sockets with a built-in CMOS watch function, an NV RAM controller
circuit, and an embedded lithium energy source.
The sockets provide an NV RAM solution for memory sized from 2k x 8
to 512k x 8 with package sizes from 26 pins to 32 pins. When a socket
is mated with a CMOS SRAM, it provides a complete solution to problems
associated with memory volatility and uses a common energy source
to maintain time and date.
The SmartWatch ROM sockets use the embedded lithium source to maintain
the time and date only. A key feature of the SmartWatch is that the
watch function remains transparent to the RAM. The SmartWatch monitors
VCC for an out-of-tolerance condition. When such a condition occurs, an
internal lithium energy source is automatically switched on and write
protection is unconditionally enabled to prevent loss of watch and RAM
data."
There are several different versions of this part so the naming on the
chip is important.