Dallas Semiconductor DS1603 Datasheet

DS1603

Elapsed Time Counter Module

www.dalsemi.com

1

2

456

7

V

CC

NC

CLK

OSC

GND

FEATURES

§ Two 32–bit counters keep track of real time

and elapsed time

§ Counters keep track of seconds for over 125

years

§ Battery powered counter counts seconds from

the time battery is attached until V
than 2.5 volts

§ VCC powered counter counts seconds while

VCC is above 4.25 volts and retains the count
in the absence of VCC under battery backup
power

§ Clear function resets selected counter to 0

§ Read/Write serial port affords low pin count

§ Powered internally by a lithium energy cell

that provides over 10 years of operation

§ 1-byte protocol defines read/write, counter

address and software clear function

§ Self-contained crystal provides an accuracy of

±2 min per month

§ Operating temperature range of 0°C to 70°C

§ Low profile SIP module

BAT

is less

PIN ASSIGNMENT

RST

DQ

3

PIN DESCRIPTION

RST - Reset

CLK - Clock
DQ - Data Input/Output
GND - Ground
V

CC

OSC - 1 Hz Oscillator Output
NC - No Connect

- +5 Volts

DESCRIPTION

The DS1603 is a real time clock/elapsed time counter designed to count seconds when VCC power is
applied and continually count seconds under battery backup power with an additional counter regardless
of the condition of VCC. The continuous counter can be used to derive time of day, week, month, and year
by using a software algorithm. The VCC powered counter will automatically record the amount of time
that VCC power is applied. This function is particularly useful in determining the operational time of
equipment in which the DS1603 is used. Alternatively, this counter can also be used under software
control to record real time events. Communication to and from the DS1603 takes place via a 3–wire
serial port. A 1-byte protocol selects read/ write functions, counter clear functions and oscillator trim. The
device contains a 32.768 kHz crystal which will keep track of time to within ±2 min/mo. An internal
lithium energy source contains enough energy to power the continuous seconds counter for over 10 years.

OPERATION

The main elements of the DS1603 are shown in Figure 1. As shown, communications to and from the
elapsed time counter occur over a 3–wire serial port. The port is activated by driving RST to a high state.
With RST at high level 8 bits are loaded into the protocol shift register providing read/write, register

select, register clear, and oscillator trim information. Each bit is serially input on the rising edge of the

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clock input. After the first eight clock cycles have loaded the protocol register with a valid protocol
additional clocks will output data for a read or input data for a write. VCC must be present to access the
DS1603. If VCC < the internal power supply (approximately 3.0 volts) the DS1603 will switch to internal
power and disable the serial port to conserve energy. When running off of the internal power supply, only
the continuous counter will continue to count and the counter powered by VCC will stop, but retain the
count which had accumulated when VCC power was lost.

PROTOCOL REGISTER

The protocol bit definition is shown in Figure 2. Valid protocols and the resulting actions are shown in
Table 1. Each data transfer to the protocol register designates what action is to occur. As defined, the
MSB (bit 7 which is designated ACC) selects the 32–bit continuous counter for access. If ACC is a
logical 1 the continuous counter is selected and the 32 clock cycles that follow the protocol will either
read or write this counter. If the counter is being read, the contents will be latched into a different register
at the end of protocol and the latched contents will be read out on the next 32 clock cycles. This avoids
reading garbled data if the counter is clocked by the oscillator during a read. Similarly, if the counter is to
be written, the data is buffered in a register and all 32 bits are jammed into the counter simultaneously on
the rising edge of the 32nd clock. The next bit (bit 6 which is designated AVC) selects the 32–bit V
active counter for access. If AVC is a logical 1 this counter is selected and the 32 clock cycles that follow
will either read or write this counter. If both bit 7 and bit 6 are written to a logic high, all clock cycles
beyond the protocol are ignored and bit 5, 4, and 3 are loaded into the oscillator trim register. A value of
binary 3 (011) will give a clock accuracy of ±120 seconds per month at 25°C. Increasing the binary
number towards 7 will cause the real time clock to run faster. Conversely, lowering the binary number
towards 0 will cause the clock to run slower. Binary 000 will stop the oscillator completely. This feature
can be used to conserve battery life during storage. In this mode the internal power supply current is
reduced to 100 nA maximum. In applications where oscillator trimming is not practical or not needed, a
default setting of 011 is recommended. Bit 2 of protocol (designated CCC) is used to clear the continuous

counter. When set to logic 1, the continuous counter will reset to 0 when RST is taken low. Bit 1 of
protocol (designated CVC) is used to clear the VCC active counter. When set to logical 1, the VCC active

CC

counter will reset to 0 when RST is taken low. Both counters can be reset simultaneously by setting CCC
and CVC both to a logical 1. Bit 0 of the protocol (designated RD) determines whether the 32 clocks to
follow will write a counter or read a counter. When RD is set to a logical 0 a write action will follow
when RD is set to a logical 1 a read action will follow. When sending the protocol, 8 bits should always
be sent. Sending less than 8 bits can produce erroneous results. If clearing the counters or trimming the
oscillator, the data transfer can be terminated after the 8–bit protocol is sent. However, when reading or
writing the counters, 32 clock cycles should always follow the protocol.

RESET AND CLOCK CONTROL

All data transfers are initiated by driving the RST input high. The RST input has two functions. First,

RST turns on the serial port logic which allows access to the protocol register for the protocol data entry.

Second, the RST signal provides a method of terminating the protocol transfer or the 32–bit counter
transfer. A clock cycle is a sequence of a falling edge followed by a rising edge. For write inputs, data
must be valid during the rising edge of the clock. Data bits are output on the falling edge of the clock

when data is being read. All data transfers terminate if the RST input is transitioned low and the DQ pin
goes to a high impedance state. RST should only be transitioned low while the clock is high to avoid

disturbing the last bit of data. All data transfers must consist of 8 bits when transferring protocol only or 8
+ 32 bits when reading or writing either counter. Data transfer is illustrated in Figure 3.

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DS1603

DATA INPUT

Following the 8–bit protocol that inputs write mode, 32 bits of data are written to the selected counter on
the rising edge of the next 32 CLK cycles. After 32 bits have been entered any additional CLK cycles will

be ignored until RST is transitioned low to end data transfer and then high again to begin new data
transfer.

DATA OUTPUT

Following the eight CLK cycles that input read mode protocol, 32 bits of data will be output from the
selected counter on the next 32 CLK cycles. The first data bit to be transmitted from the selected 32–bit
counter occurs on the falling edge after the last bit of protocol is written. When transmitting data from

the selected 32–bit counter, RST must remain at high level as a transition to low level will terminate data
transfer. Data is driven out the DQ pin as long as CLK is low. When CLK is high the DQ pin is tristated.

OSCILLATOR OUTPUT

Pin 6 of the DS1603 module is a 1 Hz output signal. This signal is present only when VCC is applied and
greater than the internal power supply. However, the output is guaranteed to meet TTL requirement only
while V
some applications.

is within normal limits. This output can be used as a 1-second interrupt or time tick needed in

CC

INTERNAL POWER

The internal battery of the DS1603 module provides 35 mAh and will run the elapsed time counter for
over 10 years in the absence of power.

DS1603 ELAPSED TIME COUNTER BLOCK DIAGRAM Figure 1

PROTOCOL BIT MAP Figure 2

7 6 5 4 3 2 1 0

ACC AVC OSC2 OSC1 OSC0 CCC CVC RD

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