Rainbow Electronics DS1678 - Manual (Page 2)

DS1678
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DESCRIPTION
The DS1678 Real-Time Clock Event Recorder records the time and date of a non-periodic, asynchronous
event each time the
INT pin is activated. The device records the seconds, minutes, hours, date, day of the
week, month, year, and century when the first event occurs. Subsequent events trigger the recording of
the 16-bit elapsed time counter (ETC) into the 2048 bytes of event log memory. This allows for up to
1025 events to be logged.
The event count register contains the total number of events that have been logged in the current event-
logging mission. The event count register also allows the user to determine if the data in the event log
memory has rolled over.
Three resolution options allow users to maximize the event log resolution while providing an adequate
maximum time between events without using extra memory locations based on the specific
characteristics of the event being logged. The seconds resolution provides the time of an event down to
the second while allowing up to 18.2 hours between events without using extra memory locations. The
minutes resolution provides the time of an event down to the minute while allowing up to 45.5 days
between events without using extra memory locations. The hours resolution provides the time of an event
down to the hour in which it occurred, while allowing up to 7.5 years between events without using extra
memory locations. Based on the expected frequency of events, the correct setting can be easily selected
to maximize the resolution and memory utilization.
The event can be triggered in three different ways depending on how the user programs the trigger select
(TRx) bits in the control register. The event can be triggered by a falling edge on the
INT pin only, a
rising edge only, or it can be triggered by rising and falling edges. Triggering with both the rising and
falling edges allows for monitoring when something is turned on/off and how long it is in either state.
The RTC provides seconds, minutes, hours, day, date, month, and year information with leap-year
compensation, year 2000-compliance, and also provides an alarm interrupt. The 2-wire interface allows
the RTC to function as a stand alone RTC in the system.
The programmable alarm trip points in the RTC will allow a flag to be set in the control register when the
specified time in the alarm trip point register is reached. The flag is readable via the 2-wire interface
during an event logging mission or, when the DS1678 is not in a mission, the
INT pin will become an
output and generate an alarm interrupt if the value in the RTC equals the value in the RTC alarm register
and the duration interval select (DISx) bits are both set to zeros.
The DS1678 operates as a slave device on the 2-wire serial bus. Access is obtained by implementing a
START condition and providing a device identification code followed by a register address. All data is
transferred to and from the DS1678 most significant bit (MSB) first. The address counter will
automatically increment so that subsequent registers can be accessed sequentially until a STOP condition
is executed. When V
CC
falls below 1.25 x V
BAT
the device automatically write protects itself, terminates
any access in progress and resets the device address counter. Inputs to the device via the 2-wire bus will
not be recognized at this time to prevent erroneous data from being written to the device from an out of
tolerance system. When V
CC
falls below V
BAT
the device switches into a low-current battery backup
mode. Upon power-up, the device switches from battery power to V
CC
when V
CC
is greater than
V
BAT
+ 0.2V and recognizes inputs from the system when V
CC
is greater than 1.25 x V
BAT
by releasing
control of the write protection on the 2-wire bus.