View ds1270w datasheet:

DS1270W 3.3V 16Mb Nonvolatile SRAM www.maxim-ic.com FEATURES PIN ASSIGNMENT Five years minimum data retention in the NC 1 36 VCC absence of external power A20 2 35 A19 A18 3 34 NC Data is automatically protected during power A16 4 33 A15 loss A17 A14 5 32 Unlimited write cycles A12 6 31 WE A7 A13 Low-power CMOS operation 7 30 A6 8 29 A8 Read and write access times as fast as 100ns A5 A9 9 28 Lithium energy source is electrically A4 10 27 A11 disconnected to retain freshness until power is A3 11 26 OE 12 25 A2 A10 applied for the first time 13 24 A1 CE Optional industrial (IND) temperature range 14 23 A0 DQ7 of -40 C to +85 C DQ0 15 22 DQ6 DQ5 DQ1 16 21 17 20 DQ2 DQ4 18 19 GND DQ3 36-Pin Encapsulated Package 740mil Extended PIN DESCRIPTION