DS1678S/T&R【PDF 6/25 页】IC RECORDER REALTIME EVENT 8SOIC

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DS1678 Real-Time Event Recorder

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ROLLOVER HANDLING

There are two options for dealing with the potential occurrence of a data overrun (i.e., more than 1024

total event logs in the event-log memory) (Figure 4). The first option is to enable rollovers. This is

accomplished by setting the rollover bit (bit 3 of the Control Register) to one. When rollover is enabled,

new data is written over previous data, starting with the Start Time Stamp Register, as if a new mission is

starting.

When a rollover occurs, the Event 0 Rollover Stamp has the elapsed time since event 1024 of the event-

log memory. This is to allow the user to recover the information recorded prior to the rollover. At the start

of a mission, the Event 0 Rollover Stamp data is zero, as there was no previous event from which to have

an elapsed time.

When 1024 events are recorded in the event-log memory, the next event causes a new time/date stamp to

be written to the Start Time Stamp Register and the elapsed time since event 1024 written to the event 0

rollover stamp. The new event is written to the first location in the event log, overwriting the old data, and

the address pointer is incremented. When the rollover occurs, the rollover flag (ROF) in the Control

The second option for dealing with data overrun is to disable rollovers by setting the rollover bit to 0. The

DS1678 stops recording after event 1025, and the address pointer is incremented from 07FFh to 0000h.

The device continues monitoring

INT and the event counter continues to increment when INT is

activated, even though the event-log memory has been filled.

A time stamp for the first event is recorded after a mission begins. The time of acquisition for subsequent

events is determined by considering the start time recorded by the time stamp; the value in the Event

Counter Register, ROF; and the address of the particular data sample in the event-log memory.

If no rollover has occurred in the event-log memory (ROF = 0), the sample time associated with any

particular data point can be calculated by multiplying the sum of the elapsed time between the events up

to that event by one second, minute, or hour depending on which resolution is selected in the DISx bits of

the Control Register, and adding this elapsed time to the value in the Start Time Stamp Register.

If rollover has been enabled, the user can determine if rollover has occurred by reading the value in the

Event Counter Register or the ROF. The Event Counter Register counts the total number of events that

have been acquired. If this value is greater than 0400h (decimal 1025), then the user knows that rollover

has occurred. If rollover has occurred, the user needs to determine how many times rollover occurred in

determining the sample time for any particular data sample. The address pointer points to the oldest data

in the event-log memory, and, if the memory has rolled over at least one time, the rollover flag is set to

one.

The DS1678 has been designed so the user cannot directly write to the event-log memory. This prevents

writing invalid data to the event-log registers.

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