19-5266 Rev 5/10 DS1642 Nonvolatile Timekeeping RAM www.maxim-ic.com FEATURES PIN CONFIGURATION Integrated NV SRAM, Real-Time Clock, TOP VIEW Crystal, Power-Fail Control Circuit, and Lithium Energy Source V A7 1 24 CC Standard JEDEC Bytewide 2k x 8 Static DS1642 A6 2 23 A8 RAM Pinout Clock Registers are Accessed Identically to A5 3 22 A9 the Static RAM. These Registers are A4 4 21 WE Resident in the Eight Top RAM Locations A3 5 20 OE Totally Nonvolatile with Over 10 Years of A2 6 19 A10 Operation in the Absence of Power Access Times of 85ns and 100ns A1 7 18 CE Quartz Accuracy 1 Minute a Month at A0 8 17 DQ7 +25C, Factory Calibrated 16 DQ6 DQ0 9 BCD-Coded Year, Month, Date, Day, Hours, 15 DQ5 Minutes, and Seconds with Leap Year DQ1 10 Compensation Valid Up to 2100 14 DQ4 DQ2 11 Power-Fail Write Protection Allows for 13 DQ3 GND 12 10% V Power Supply Tolerance CC Lithium Energy Source is Electrically Disconnected to Retain Freshness Until ENCAPSULATED DIP Power is Applied for the First Time UL Recognized ORDERING INFORMATION VOLTAGE PART TEMP RANGE PIN-PACKAGE TOP MARK RANGE (V) DS1642-85+ 5.0 0C to +70C 24 EDIP (0.720a) DS1642+85 DS1642-100+ 5.0 0C to +70C 24 EDIP (0.720a) DS1642+100 +Denotes a lead(Pb)-free/RoHS-compliant package. A indicates a lead(Pb)-free product. The top mark will include a + symbol on lead-free devices. 1 of 11 DS1642 PIN DESCRIPTION PIN NAME FUNCTION 1 A7 2 A6 3 A5 4 A4 5 A3 6 A2 Address Input 7 A1 8 A0 19 A10 22 A9 23 A8 9 DQ0 10 DQ1 11 DQ2 13 DQ3 Data Input/Output 14 DQ4 15 DQ5 16 DQ6 17 DQ7 12 GND Ground 18 CE Active-Low Chip-Enable Input 20 OE Active-Low Output-Enable Input 21 WE Active-Low Write-Enable Input 24 V Power-Supply Input CC DESCRIPTION The DS1642 is a 2k x 8 nonvolatile static RAM and a full-function real-time clock (RTC), both of which are accessible in a bytewide format. The nonvolatile time keeping RAM is pin and function equivalent to any JEDEC-standard 2k x 8 SRAM. The device can also be easily substituted in ROM, EPROM, and EEPROM sockets, providing read/write nonvolatility and the addition of the real-time clock function. The real-time clock information resides in the eight uppermost RAM locations. The RTC registers contain year, month, date, day, hours, minutes, and seconds data in 24-hour BCD format. Corrections for the day of the month and leap year are made automatically. The RTC clock registers are double-buffered to avoid access of incorrect data that can occur during clock update cycles. The double-buffered system also prevents time loss as the timekeeping countdown continues unabated by access to time register data. The DS1642 also contains its own power-fail circuitry, which deselects the device when the V supply is in CC an out-of-tolerance condition. This feature prevents loss of data from unpredictable system operation brought on by low V as errant access and update cycles are avoided. CC 2 of 13