DS1678S Maxim Integrated Products, DS1678S Datasheet - Page 13

• Manufacturer Part Number: DS1678S
• Description: IC RECORDER REALTIME EVENT 8SOIC
• Manufacturer: Maxim Integrated Products
• Type: Time Event Recorderr

Specifications of DS1678S

• Memory Size: 32B
• Time Format: HH:MM:SS (12/24 hr)
• Date Format: YY-MM-DD-dd
• Interface: I²C, 2-Wire Serial
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (5.3mm Width), 8-SOP, 8-SOEIAJ
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

DS1678
CLR - Clear Enable – This bit enables the memory to be cleared. When this bit is set to a one and the
clear memory (CM) bit in the status register is subsequently written to a 1, the event log memory, event
count, and start time stamp registers are all cleared to zeros. Following the writing of a 1 to the ME bit,
the CLR bit is also cleared to zero. If the clear enable bit is set, but a command other than writing a 1 to
the clear memory bit is issued next, the CLR bit is cleared to a zero and the contents of the event log,
start time stamp, and event counter register are unchanged.
DIS1, DIS0 - Duration Interval Select [0-1] – These bits select the amount of time between increments
of the elapsed time counter that is used to determine the amount of time between events. After the first
event is recorded, all subsequent events are recorded as the elapsed time since the previous event. When
a subsequent event occurs, the ETC value is stored in the event log memory.
In order to obtain the maximum accuracy of the event logger, the smallest possible resolution of the ETC
should be selected. The expected maximum time between events must also be taken into account in order
to get the full 1025 events logged because when the ETC count reaches 65535 increments, if the next
event has not occurred by that point in time, FFh will be written into the memory, the ETC will roll over
to 00h and continue to count until the next event occurs or FFh is reached again. Whenever FFh is
reached by the ETC, it will store that value in event log memory, reset to 00h, continue counting, and the
memory address pointer will increment to the next memory location. When ever an FFh appears in the
memory, the next two bytes of data will be part of the elapsed time for the same event, even if the value
in the next two bytes of memory are 00h which means that an event occurred at time increment FFh. In
order to recover the total elapsed time between events when a FFh is in the Event Log Memory; simply
add the contents of the next two bytes to the FFh. If the next two bytes are 00h indicating that the event
occurred at FFh, by adding the 00h in the next two bytes, you will end up with FFh. If the next two bytes
are 01h, you will get 100h when the data is added to FFh. This will represent the total elapsed time since
the previous event. The event counter will not be incremented when the ETC rolls over since a new event
has not occurred.
The ETC will be incremented as the selected single seconds, minutes, or hours byte of the RTC
increments to prevent time losses from short duration events. Since the time base in the RTC continues to
run, even when the ETC is cleared to prepare for a new event, and the ETC is incremented every time the
selected byte in the RTC increments, the actual time resolution will not be lost even when events occur
more frequently than the minimum time resolution selected. If an event occurs half way between
increments of the ETC, then the first increment of the next event will occur when the seconds, minutes or
hours register increments next, thus preserving the correct time to the resolution selected in the DISx bits.
The user can select one of the settings in Table 2.
When the Alarm Interrupt Output is to be used, the DISx bits should be set to zeros, which will disable
the ETC and the rest of the event logger circuitry to conserve battery life. An event-logging mission can
not be started if the DISx bits are both set to zero. This will enable the Alarm Flag to generate an Alarm
Interrupt via the
output pin.
INT
With the DIS0 bit set to a one and the DIS1 bit set to zero, the ETC will increment every time the single
seconds byte in the RTC is incremented. This will give the maximum resolution between events, but
since the counter is limited to only 16 bit and will roll over to the next two memory bytes when it reaches
the maximum value, the largest interval between events that can be accurately measured without using
additional memory space and reducing the total number of events able to be logged is 65,535 seconds or
about 18.2 hours. If the maximum time between events could be greater than 18.2 hours, you should
consider using one of the courser resolutions to conserve memory.
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