PDF DS12C887 Data sheet ( Hoja de datos )

Número de pieza	DS12C887
Descripción	(DS12xxx) Real Time Clock
Fabricantes	Maxim Integrated Products
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No Preview Available ! Rev 0; 6/05 Real-Time Clock General Description Features The DS12885, DS12887, and DS12C887 real-time clocks (RTCs) are designed to be direct replacements for the DS1285 and DS1287. The devices provide a ♦ Drop-In Replacement for IBM AT Computer Clock/Calendar real-time clock/calendar, one time-of-day alarm, three ♦ RTC Counts Seconds, Minutes, Hours, Day, Date, maskable interrupts with a common interrupt output, a Month, and Year with Leap Year Compensation programmable square wave, and 114 bytes of battery- backed static RAM (113 bytes in the DS12C887 and DS12C887A). The DS12887 integrates a quartz crystal and lithium energy source into a 24-pin encapsulated mDIP package. The DS12C887 adds a century byte at address 32h. For all devices, the date at the end of the omonth is automatically adjusted for months with fewer .cthan 31 days, including correction for leap years. The devices also operate in either 24-hour or 12-hour format with an AM/PM indicator. A precision temperature-compensated circuit monitors the status of UVCC. If a primary power failure is detected, the device t4automatically switches to a backup supply. A lithium coin-cell battery can be connected to the VBAT input pin on the DS12885 to maintain time and date operation ewhen primary power is absent. The device is accessed through a multiplexed byte-wide interface, which sup- eports both Intel and Motorola modes. hApplications Embedded Systems SUtility Meters taSecurity Systems Network Hubs, Bridges, and Routers aTypical Operating Circuit .DCRYSTAL VCC www eet4U.comDS83C520 X1 X2 AS VCC RESET R/W RCLR DS CS DS12885 AD(0–7) SQW IRQ VBAT MOT GND Through 2099 ♦ Binary or BCD Time Representation ♦ 12-Hour or 24-Hour Clock with AM and PM in 12-Hour Mode ♦ Daylight Saving Time Option ♦ Selectable Intel or Motorola Bus Timing ♦ Interfaced with Software as 128 RAM Locations ♦ 14 Bytes of Clock and Control Registers ♦ 114 Bytes of General-Purpose, Battery-Backed RAM (113 Bytes in the DS12C887 and DS12C887A) ♦ RAM Clear Function (DS12885, DS12887A, and DS12C887A) ♦ Interrupt Output with Three Independently Maskable Interrupt Flags ♦ Time-of-Day Alarm Once Per Second to Once Per Day ♦ Periodic Rates from 122µs to 500ms ♦ End-of-Clock Update Cycle Flag ♦ Programmable Square-Wave Output ♦ Automatic Power-Fail Detect and Switch Circuitry ♦ Optional 28-Pin PLCC Surface Mount Package or 32-Pin TQFP (DS12885) ♦ Optional Encapsulated DIP (EDIP) Package with Integrated Crystal and Battery (DS12887, DS12887A, DS12C887, DS12C887A) ♦ Optional Industrial Temperature Range Available ♦ Underwriters Laboratory (UL) Recognized ataShPin Configurations and Ordering Information appear at end of data sheet. .D______________________________________________ Maxim Integrated Products 1 wwFor pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at w1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 page AS tASD DS R/W CS AD0–AD7 PWASH PWASL tASD tASL tCYC tASED Real-Time Clock Intel Bus Read Timing PWEH tCS tAHL tDDR tCH tDHR IRQ Release Delay Timing DS RESET IRQ tIRDS tEWL tIRB VCC VPF(MAX) VPF(MIN) tF Power-Up/Power-Down Timing tR tRPU INPUTS RECOGNIZED OUTPUTS VALID DON'T CARE HIGH-Z RECOGNIZED VALID _____________________________________________________________________ 5 5 Page Real-Time Clock Detailed Description The DS12885 family of RTCs provide 14 bytes of real- time clock/calendar, alarm, and control/status registers and 114 bytes (113 bytes for DS12C887 and DS12C887A) of nonvolatile, battery-backed static RAM. A time-of-day alarm, three maskable interrupts with a common interrupt output, and a programmable square- wave output are available. The devices also operate in either 24-hour or 12-hour format with an AM/PM indica- tor. A precision temperature-compensated circuit moni- tors the status of VCC. If a primary power-supply failure is detected, the devices automatically switch to a back- up supply. The backup supply input supports a primary battery, such as lithium coin cell. The devices are accessed through a multiplexed address/data bus that supports Intel and Motorola modes. Oscillator Circuit The DS12885 uses an external 32.768kHz crystal. The oscillator circuit does not require any external resistors or capacitors to operate. Table 1 specifies several crys- tal parameters for the external crystal. Figure 1 shows a functional schematic of the oscillator circuit. An enable bit in the control register controls the oscillator. Oscillator startup times are highly dependent upon crystal characteristics, PC board leakage, and layout. High ESR and excessive capacitive loads are the major contributors to long startup times. A circuit using a crystal with the recommended characteristics and proper layout usually starts within one second. An external 32.768kHz oscillator can also drive the DS12885. In this configuration, the X1 pin is connected to the external oscillator signal and the X2 pin is floated. Table 1. Crystal Specifications* PARAMETER SYMBOL MIN TYP MAX UNITS Nominal Frequency fO 32.768 kHz Series Resistance ESR 50 kΩ Load Capacitance CL 6 pF *The crystal, traces, and crystal input pins should be isolated from RF generating signals. Refer to Application Note 58: Crystal Considerations for Dallas Real-Time Clocks for additional specifications. COUNTDOWN CHAIN CL1 CL2 RTC REGISTERS DS12885 X1 X2 CRYSTAL Figure 1. Oscillator Circuit Showing Internal Bias Network ____________________________________________________________________ 11 11 Page

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