DS1486 Datasheet, PDF (3/17 Pages) Dallas Semiconductor – RAMified Watchdog Timekeeper

DS1486/DS1486P
DATA RETENTION
The RAMified Timekeeper provides full functional capability when V_CC is greater than 4.5 volts and
write-protects the register contents at 4.25 volts typical. Data is maintained in the absence of V_CC without
any additional support circuitry. The DS1486 constantly monitors V_CC. Should the supply voltage decay,
the RAMified Timekeeper will automatically write-protect itself and all inputs to the registers become
“don’t care.” The two interrupts INTA and INTB (INTB) and the internal clock and timers continue to run
regardless of the level of V_CC. However, it is important to insure that the pull-up resistors used with the
interrupt pins are never pulled up to a value that is greater than V_CC + 0.3V. As V_CC falls below
approximately 3.0 volts, a power switching circuit turns the internal lithium energy source on to maintain
the clock and timer data functionality. It is also required to insure that during this time (battery backup
mode), the voltage present at INTA and INTB (INTB) never exceeds V_BAT. During power-up, when V_CC
rises above approximately 3.0 volts, the power switching circuit connects external V_CC and disconnects
the internal lithium energy source. Normal operation can resume after V_CC exceeds 4.5 volts for a period
of 200 ms.
RAMIFIED TIMEKEEPER REGISTERS
The RAMified Timekeeper has 14 registers which are 8 bits wide that contain all of the timekeeping,
alarm, watchdog and control information. The clock, calendar, alarm, and watchdog registers are memory
locations which contain external (user-accessible) and internal copies of the data. The external copies are
independent of internal functions except that they are updated periodically by the simultaneous transfer of
the incremented internal copy (see Figure 1). The Command Register bits are affected by both internal
and external functions. This register will be discussed later. Registers 0, 1, 2, 4, 6, 8, 9, and A contain
time of day and date information (see Figure 2). Time of day information is stored in BCD. Registers 3,
5, and 7 contain the Time of Day Alarm information. Time of Day Alarm information is stored in BCD.
Register B is the Command Register and information in this register is binary. Registers C and D are the
Watchdog Alarm Registers and information which is stored in these two registers is in BCD. Registers E
through 1FFFF are user bytes and can be used to maintain data at the user’s discretion.
CLOCK ACCURACY (DIP MODULE)
The DS1486 is guaranteed to keep time accuracy to within ±1 minute per month at 25°C.
CLOCK ACCURACY (POWERCAP MODULE)
The DS1486P and DS9034PCX are each individually tested for accuracy. Once mounted together, the
module is guaranteed to keep time accuracy to within ±1.53 minutes per month (35 ppm) at 25°C.
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