View ds1258w datasheet:

DS1258W 3.3V 128k x 16 Nonvolatile SRAM www.maxim-ic.com FEATURES PIN ASSIGNMENT 10-year minimum data retention in the CEU 1 40 VCC absence of external power CEL 2 39 WE DQ15 3 38 A16 Data is automatically protected during a DQ14 4 37 A15 power loss A14 DQ13 5 36 Separate upper byte and lower byte chip DQ12 6 35 A13 DQ11 A12 select inputs 7 34 DQ10 8 33 A11 Unlimited write cycles DQ9 A10 9 32 Low-power CMOS DQ8 10 31 A9 Read and write access times as fast as 100ns GND 11 30 GND 12 29 DQ7 A8 Lithium energy source is electrically 13 28 DQ6 A7 disconnected to retain freshness until power is 14 27 DQ5 A6 applied for the first time DQ4 15 26 A5 A4 DQ3 16 25 17 24 DQ2 A3 18 23 DQ1 A2 DQ0 19 22 A1 OE 20 21 A0 40-PIN Encapsulated Package 740-Mil