DS1678S Maxim Integrated Products, DS1678S Datasheet - Page 14

• 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

With the DIS0 bit set to a zero and the DIS1 bit set to a one, the ETC will increment every time the
single minutes byte in the RTC is incremented. This will give a medium resolution between events, but
will increase the largest possible interval between events that can be accurately measured without using
additional memory space and reducing the total number of events able to be logged to 65,535 minutes or
about 45.5 days. If the maximum time between events could be greater than 45.5 days, you should
consider using one of the courser resolutions to conserve memory.
With both of the DISx bits set to a one, the ETC will increment every time the single hours byte in the
RTC is incremented. This will give the lowest resolution between events, but will increase the largest
possible interval between events that can be accurately measured without using additional memory space
and reducing the total number of events able to be logged to 65,535 hours or about 7.5 years.
In the event that a second event occurs before the ETC is able to increment for the first time, all zeros
will be logged in the event log memory and the ETC will be reset. If this occurs, the time base will
remain correct since it is based on the separate RTC incrementing, but the exact time of the event will be
no more accurate than the size of the time increment that is chosen. For this reason, it is recommended to
use the finest resolution possible for your logging to minimize the errors. If the normal duration between
events is several days or months, then a few minutes or an hour may not be significant to your data
accuracy.
As an example, an event occurs after 28h hours which causes the ETC to be reset. The ETC is set to
increment on the hour, but the next event happens after 45 minutes. The value recorded in the event log
memory is 00h, the event counter is incremented, and the ETC is cleared to begin counting for the next
event. That next event happens 20 minutes later, but the value in the ETC is 01h because the RTC
incremented the ETC on the hour, which was 15 minutes after the last event was recorded in the event
log memory. We now know that in the course of about an hour three events took place. If this is normal,
then we should have chosen a finer resolution, but this does sometimes happen, even when events are
normally spread widely apart. We did not loose any data in our example because we know in which hour
the events took place and when we chose the resolution, we decided that knowing which hour was
accurate enough for our needs. The RTC maintained the correct time base, even though the ETC was
cleared before it was incremented even once for the second event in our example. The third event
incremented after only 15 minutes, but, relative to the first event in our example, this was correct because
the second event occurred after 45 minutes, and the third event was incremented after an additional
15 minutes, which makes one hour.
DURATION INTERVAL SELECT BITS Table 2
RO - Roll-Over – This bit determines whether the datalog function of the DS1678 rolls over or stops
writing data to the event log memory if the event log memory is completely filled. If RO is set to a 1, the
event log memory will “roll over” after all 2048 bytes in the event log memory have been used. In other
words, after the 1024th event recorded in the event log memory, the following sample will have the full
time/date stamp information written to the start time stamp register and the contents of the ETC written to
the 2-byte following the start time stamp (event 0 elapsed time from last event) and the next sample will
have the duration of time from the new start time stamp value written to event log memory address
DIS1
0
0
1
1
DIS0
0
1
0
1
The Counter will Increment Every Second
The Counter will Increment Every Minute
The Counter will Increment Every Hour
Alarm Interrupt Output Enabled
ELAPSED TIME COUNT
RESOLUTION
14 of 26
MAX. TIME BETWEEN
18.2 Hours
45.5 Days
EVENTS
7.5 Years