View ds1647 d datasheet:

DS1647/DS1647P Nonvolatile Timekeeping RAM www.maxim-ic.com FEATURES PIN ASSIGNMENT Integrates NV SRAM, real-time clock, A18 1 32 VCC crystal, power-fail control circuit and lithium A16 31 A15 2 energy source A14 3 30 A17 Clock registers are accessed identically to the A12 4 29 WE A13 A7 5 28 static RAM. These registers are resident in A6 6 27 A8 the eight top RAM locations A5 A9 7 26 Totally nonvolatile with over 10 years of A4 8 25 A11 A3 OE operation in the absence of power 9 24 A2 10 23 A10 BCD coded year, month, date, day, hours, CE A1 11 22 minutes, and seconds with leap year 12 21 A0 DQ7 compensation valid up to 2100 13 20 DQ0 DQ6 Power-fail write protection allows for ±10% 14 19 DQ1 DQ5 VCC power supply tolerance DQ2 15 18 DQ4 DS1647 o