19-5501 Rev 9/10 DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM www.maxim-ic.com FEATURES PIN CONFIGURATION Integrated NV SRAM, Real-Time Clock TOP VIEW (RTC), Crystal, Power-Fail Control Circuit, and Lithium Energy Source 34 A18 IRQ/FT 1 Maxim A15 2 33 A17 Clock Registers are Accessed Identically to A16 3 DS1557 32 A14 31 RST 4 A13 the Static RAM These Registers Reside in the V 30 CC 5 A12 6 29 A11 16 Top RAM Locations WE 7 28 A10 OE 27 8 A9 Century Byte Register (i.e., Y2K Compliant) CE 26 9 A8 DQ7 25 10 A7 DQ6 Totally Nonvolatile with Over 10 Years of 24 A6 11 DQ5 23 A5 12 DQ4 Operation in the Absence of Power 22 13 A4 DQ3 14 21 A3 DQ2 Precision Power-On Reset 20 15 A2 DQ1 19 16 A1 DQ0 Programmable Watchdog Timer and RTC X1 GND V X2 BAT 18 17 A0 GND Alarm PowerCap Module Board BCD-Coded Year, Month, Date, Day, Hours, (Uses DS9034PCX PowerCap) Minutes, and Seconds with Automatic Leap Year Compensation Valid Up to the Year PIN DESCRIPTION 2100 A0A18 - Address Input Battery Voltage-Level Indicator Flag DQ0DQ7 - Data Input/Outputs Power-Fail Write Protection Allows for 10% IRQ/FT - Interrupt, Frequency Test V Power-Supply Tolerance Output (Open Drain) CC RST - Power-On Reset Output Lithium Energy Source is Electrically (Open Drain) Disconnected to Retain Freshness Until Power CE - Chip Enable is Applied for the First Time OE - Output Enable Also Available in Industrial Temperature WE - Write Enable Range: -40C to +85C V - Power-Supply Input CC GND - Ground X1, X2 - Crystal Connection V - Battery Connection BAT Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata. 1 of 17 DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM ORDERING INFORMATION VOLTAGE PART TEMP RANGE PIN-PACKAGE TOP MARK** (V) DS1557P-70+ 0C to +70C 5.0 34 PowerCap* DS1557P+70 DS1557P-70IND+ -40C to +85C 5.0 34 PowerCap* DS1557P+70 IND DS1557WP-120+ 0C to +70C 3.3 34 PowerCap* DS1557WP+120 DS1557WP-120IND+ -40C to +85C 3.3 34 PowerCap* DS1557WP+120 IND + Denotes a lead(Pb)-free/RoHS-compliant package. *DS9034PCX+ or DS9034I-PCX+ (PowerCap) required. Must be ordered separately. *An IND on the top mark denotes an industrial temperature grade device. DESCRIPTION The DS1557 is a full-function, year-2000-compliant (Y2KC), real-time clock/calendar (RTC) with an RTC alarm, watchdog timer, power-on reset, battery monitor, and 512k x 8 nonvolatile static RAM. User access to all registers within the DS1557 is accomplished with a byte-wide interface as shown in Figure 1. The RTC registers contain century, year, month, date, day, hours, minutes, and seconds data in 24-hour BCD format. Corrections for day of month and leap year are made automatically. The RTC registers are double-buffered into an internal and external set. The user has direct access to the external set. Clock/calendar updates to the external set of registers can be disabled and enabled to allow the user to access static data. Assuming the internal oscillator is turned on, the internal set of registers is continuously updated this occurs regardless of external registers settings to guarantee that accurate RTC information is always maintained. The DS1557 has interrupt (IRQ/FT) and reset (RST) outputs which can be used to control CPU activity. The IRQ/FT interrupt output can be used to generate an external interrupt when the RTC register values match user programmed alarm values. The interrupt is always available while the device is powered from the system supply and can be programmed to occur when in the battery-backed state to serve as a system wakeup. Either the IRQ/FT or RST outputs can also be used as a CPU watchdog timer, CPU activity is monitored and an interrupt or reset output will be activated if the correct activity is not detected within programmed limits. The DS1557 power-on reset can be used to detect a system power down or failure and hold the CPU in a safe reset state until normal power returns and stabilizes the RST output is used for this function. The DS1557 also contains its own power-fail circuitry, which automatically deselects the device when the V supply enters an out-of-tolerance condition. This feature provides a high degree of data security CC during unpredictable system operation brought on by low V levels. CC 2 of 17