DS1500_11 MAXIM [Maxim Integrated Products], DS1500_11 Datasheet - Page 17

• Manufacturer Part Number: DS1500_11
• Description: Y2K Watchdog RTC with Nonvolatile Control
• Manufacturer: MAXIM [Maxim Integrated Products]

DS1500 Y2K Watchdog RTC with Nonvolatile Control
regardless of the state of the watchdog enable (WDE) bit, to serve as an indication to the processor that a
watchdog timeout has occurred. The watchdog timer operates in two modes, repetitive and single-shot.
If WDE is 1 and the watchdog steering bit (WDS) is 0, the watchdog is in repetitive mode. When the watchdog
times out, both WDF and IRQF are set. IRQ goes active and IRQF goes to 1. The watchdog timer is reloaded when
the processor performs a write of the watchdog registers and the timeout period restarts. Reading the control A
register clears the IRQ flag.
If WDE and WDS are 1, the watchdog is in single-shot mode. When the watchdog times out, RST goes active for a
period of t
. When RST goes inactive, WDE resets to 0. Writing a value of 00h to both watchdog registers
REC
disables the watchdog timer. The watchdog function is automatically disabled upon power-up by the power-on
reset setting WDE = 0 and WDS = 0. The watchdog registers are not initialized at power-up and should be
initialized by the user.
Note: The TE bit must be used to disable transfers when writing to the watchdog registers.
The following summarizes the configurations in which the watchdog can be used:
WDE = 0 and WDS = 0: WDF is set.
WDE = 0 and WDS = 1: WDF is set.
WDE = 1 and WDS = 0: WDF and IRQF are set, and the IRQ pin is pulled low.
WDE = 1 and WDS = 1: WDF is set, the RST pin pulses low, and WDE resets to 0.
WAKEUP/KICKSTART
The DS1500 incorporates a wakeup feature, which powers on at a predetermined date by activating the PWR
output pin. In addition, the kickstart feature allows the system to be powered up in response to a low-going
transition on the KS pin, without operating voltage applied to the V
pin. As a result, system power can be applied
CCI
upon such events as key closure, or a modem-ring-detects signal. To use either the wakeup or the kickstart
features, the DS1500 must have an auxiliary battery connected to the V
pin, and the oscillator must be running.
BAUX
The wakeup feature is controlled through the time-of-day/date power-enable bit (TPE). Setting TPE to 1 enables
the wakeup feature. Transfers (TE) must be enabled for a wake up event to occur. Writing TPE to 0 disables the
wakeup feature. Similarly, the kickstart feature is controlled through the kickstart interrupt-enable bit (KIE).
If the wakeup feature is enabled, while the system is powered down (no V
voltage), the clock/calendar monitors
CCI
the current day or date for a match condition with day/date alarm register (0Bh). With the day/date alarm register,
the hours, minutes, and seconds alarm bytes in the clock/calendar register map (02h, 01h, and 00h) are also
monitored. As a result, a wakeup occurs at the day or date and time specified by the day/date, hours, minutes, and
seconds alarm register values. This additional alarm occurs regardless of the programming of the TIE bit. When the
match condition occurs, the PWR pin is automatically driven low. This output can turn on the main system power
supply, which provides V
voltage to the DS1500 as well as the other major components in the system. Also, at
CCI
this time, the time-of-day/date alarm flag is set, indicating that a wakeup condition has occurred.
If V
is present, while V
is low, the KS input pin is monitored for a low-going transition of minimum pulse width
BAUX
CC
t
. When such a transition is detected, the PWR line is pulled low, as it is for a wakeup condition. Also at this
KSPW
time, KSF is set, indicating that a kickstart condition has occurred. The KS input pin is always enabled and must be
held at a valid logic level.
The timing associated with these functions is divided into five intervals, labeled 1 to 5 on the diagram.
The occurrence of either a kickstart or wakeup condition causes the PWR pin to be driven low, as described above.
During Interval 1, if the supply voltage on the V
pin rises above the greater of V
or V
before the power-on
CCI
BAT
PF
timeout period (t
) expires, then PWR remains at the active-low level. If V
does not rise above the greater of
POTO
CCI
V
or V
in this time, then the PWR output pin is turned off and returns to its high-impedance level. In this event,
BAT
PF
the IRQ pin also remains tri-stated. The interrupt flag bit (either TDF or KSF) associated with the attempted power-
on sequence remains set until cleared by software during a subsequent system power-on.
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