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Application Note 30
Recording Power Cycling
Information Using the DS1602/DS1603
www.dalsemi.com
PIN ASSIGNMENT
V
CC
RST
DQ
NC
CLK
OSC
GND
1
2
3
4
5
6
7
RST
DQ
CLK
GND
1
2
3
4
8
7
6
5
V
CC
X1
X2
V
BAT
RST
DQ
CLK
GND
1
2
3
4
8
7
6
5
V
CC
X1
X2
V
BAT
DS1602
8-Pin DIP (300
-mil)
DS1602S
8 PIN SOIC (200 mil)
DESCRIPTION
The DS1602 and DS1603 from Dallas Semiconductor offer a simplified hardware solution for keeping
time as well as tracking powered up time of a system. The DS1602 and DS1603 can be read and written
directly by a microprocessor or microcontroller using simple software; however, a more creative software
algorithm can be used to track years, months, days, day of week, time of day, etc. In addition, power–up
time and number of power–up cycles can also be tracked using the DS1602/DS1603 with appropriate
software.
The continuous counter and power–on counter in the DS1602/DS1603 are 32–bit counters which count in
seconds and can be read and written through the DS1602/DS1603 3–wire serial interface. For the most
basic implementation:
1. The continuous counter will be set once and left to increment until it reaches its maximum value;
2. The powered up counter will be initially cleared once, and left to increment until it reaches its
maximum value.
With these two assumptions, each counter has the ability to count up to a maximum value of (2
32
–1)
seconds, or 4.29 x 10
9
seconds (about 136 years).
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073099
APPLICATION NOTE 30
For a system that needs 100+ years of continuous timekeeping ability, the entire 32–bit counters may be
required; but for users where the maximum continuous counter time required could be about 5 years, the
unused counter bits space can be put to better use as memory bits for storing power–up cycling
information.
As seen in Figure 1, DS1602/DS1603 can be partitioned to provide a continuous time counter and a
power–up time counter with the capability to count up to 4.75 years, leaving the remaining higher bits of
the counter available as a read/write nonvolatile memory.
The software implementation requires the use of three registers, so a third register must be mapped into
the available two as in Figure 1.
An example of how the counters may be used to accomplish this task follows.
MAPPING THREE REGISTERS ONTO TWO
Figure 1
CONTINUOUS COUNTER MAP
Bits 1–24: Remain as continuous time base measurement, up to 16.7 x 10
6
seconds or 0.53 years.
Bit 25: Buffer or overflow bit; for when the continuous time counter reaches its maximum value and has
not been read and reset by the processor. This bit also serves to separate the counter part of the register
from the part which will be used as memory bits.
Bits 26–28: Number of years continuous time has been running x 0.53.
Bits 29–32: Number of power cycles x 128. These four bits serve as a register which is incremented once
for each full count reached in bits 26–32 of the power–up counter.
POWERED UP COUNTER MAP
Bits 1–24: Remain as nonvolatile seconds measurement of powered up seconds, storing up to 16.7 x 10
6
seconds, or 0.53 years.
Bit 25: Buffer or overflow bit; for when the power–up counter reaches its maximum value and has not
been read and reset by the processor. This bit also serves to separate the counter part of the register from
the part which will be used as memory bits.
Bits 26–32: The high 7 bits of the power–up counter are the 1-127 count storage area for the number of
power–up cycles the DS1602 or DS1603 has seen.
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APPLICATION NOTE 30
With this discipline and the proper software algorithms in place, power–on time and continuous time are
maintained by the DS1602/DS1603’ self-contained counters while the number of power–up cycles and
s
years of elapsed time x 0.53 is maintained in the higher order bits of the counters which are used as
memory.
This implementation requires that a microcontroller must be prepared to read/write the DS1602 or
DS1603 at least once every year.
For Continuous Time Tracking
When the lower 24 bits of the continuous counter have exceeded 0.53 years and set bit 25 to 1, the
controller must read the continuous counter, determine the status of bit 25, and if 1, clear the bit and
increment the value in bits 26–28 by one half-year. If bit 25 is not set, the lower 24 bits of the register
have yet to reach 0.53 years and can continue counting.
Once the value in bits 26–28 has reached 111, or 7 x 0.53 years, the continuous time counter can continue
to count up to 1.06 years in the lower 24 bits plus the overflow of 0.53 in bit 25 for a maximum value of 9
x 0.53 years.
FOR CONTINUOUS TIME TRACKING Figure 2
For Power-up Time Tracking
When the lower 24 bits of the power–up counter have exceeded 0.53 years and set bit 25 of the counter to
1, the controller must read the power–up counter, determine the status of bit 25, and if 1, clear the bit and
store the value in external memory so that the power–up counter can continue to count. The maximum
power–up time that can be stored in this way is 2 x 0.53 years within the DS1602/DS1603.
FOR POWER-UP TIME TRACKING
Figure 3
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APPLICATION NOTE 30
For Number of Power-up Cycles Tracking
Performing this function with the DS1603 or DS1602 is primarily a software task. When originally
written with a start value or cleared, bits 25–32 of the power–up counter must be set to 0. Upon each
power–up thereafter, the controller or processor connected to the DS1603 must read the power–up
counter and examine the value stored in the high 7 bits. If the value is less than 1111111, then the
controller must increment the value and write it back to the 7 higher order bits. If the value in the higher
order bits is 1111111, the controller must set the value of 0000000, read the value in the high 4 bits of the
continuous time counter, increment it by 1, and write the new value back to the high 4 bits. Using this
software algorithm, the DS1603 or DS1602 can be used to record and store up to 2,047 power cycles.
FOR NUMBER OF POWER-UP CYCLES TRACKING Figure 4
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