DS1371U+C01 - Maxim Integrated Products, Inc.

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General Description

The DS1371 is a 32-bit binary counter that is

designed to continuously count time in seconds.

An additional counter that can generate a

periodic alarm or serve as a watchdog timer is

also provided. If enabled as a watchdog timer,

the watchdog strobe input pin provides a

hardware reset of the counter. If disabled, this

counter can be used as 3 Bytes of general-

purpose RAM. A configurable output can be

used as an interrupt or provide a square wave at

one of four selectable frequencies. The device is

programmed serially through a I2C bidirectional

bus.

Applications

Servers

Point-of-Sale Equipment

Portable Instruments

Elapsed Time Measurements

Typical Operating Circuit

Features

 32-Bit Binary Counter

 24-Bit Binary Counter Provides Periodic

Alarm, Watchdog Timer, or RAM

 Strobe Input to Reset Watchdog Timer

 Single Output Configurable as Interrupt or

Square Wave

 I2C Serial Interface

 Low-Voltage Operation

 Operating Temperature Range:

-40°C to +85°C

 Available in 8-Pin μSOP

Ordering Information

PART TEMP RANGE

PIN-

PACKAGE TOP

MARK

DS1371U -40°C to +85°C 8 μSOP 1371

DS1371U+ -40°C to +85°C 8 μSOP 1371

+Denotes a lead-free/RoHS-compliant package. A + appears on the top

mark for lead-free packages.

Pin Configuration

DS1371

I2C, 32-Bit Binary Counte

Watchdo

Clock

www.maxim-ic.com

TOP VIEW

μSOP

WDS

GND

VCC

SQW/

SCL

SDA

DS1371

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ABSOLUTE MAXIMUM RATINGS

Voltage Range on VCC Pin Relative to Ground………………………………………………………..-0.3V to +6.0V

Voltage Range on SDA, SCL, and WDS Relative to Ground…………………………………..-0.3V to (VCC +0.5V)

Operating Temperature Range (noncondensing)……………………………………………………...-40°C to +85°C

Storage Temperature Range………………………………………………………………………….-55°C to +125°C

Soldering Temperature…………………………………………………………………...See IPC/JEDEC J-STD-020

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only,

and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the

specifications is not implied. Exposure to absolute maximum rating conditions for extended periods can affect device reliability.

RECOMMENDED DC OPERATING CONDITIONS

(TA = -40°C to +85°C)

PARAMETER SYMBOL MIN TYP MAX UNITS

Supply Voltage (Note 1) VCC 1.7 3.3 5.5 V

Input Logic 1 (Notes 2, 3) VIH 0.7 VCC V

CC + 0.3 V

Input Logic 0 (Notes 2, 3) VIL -0.3 0.3VCC V

DC ELECTRICAL CHARACTERISTICS

(VCC = 1.7V to 5.5V, TA = -40°C to +85°C, unless otherwise noted.) (Note 4)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage (Note 1) VCC 1.7 5.5 V

Oscillator Operating Voltage

Range (Note 1) VOSC 1.3 5.5 V

Input Leakage ILI (Note 2) 1 μA

I/O Leakage ILO (Note 3) 1 μA

VCC > 2V; VOL = 0.4V

SDA Logic 0 Output (Note 1) IOLSDA VCC < 2V; VOL = 0.2VCC 3 mA

VCC > 2V; VOL = 0.4V 3.0

1.7V < VCC < 2V;

VOL = 0.2VCC 3.0

SQW/INT Logic 0 Output

(Note 1) IOLSQW 1.3V < VCC < 1.7V;

VOL = 0.2VCC 250

μA

Active Supply Current ICCA (Note 5) 100 150 μA

Timekeeping Current

(Oscillator Enabled, INTCN = 1) IOSC0 (Notes 6, 7) 800 nA

Timekeeping Current

(Oscillator Enabled, INTCN = 0) IOSC1 (Notes 6, 7) 1300 nA

Data Retention Current

(Oscillator Disabled) IDDR (Note 6) 100 nA

DS1371

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AC ELECTRICAL CHARACTERISTICS

(VCC = 1.7V to 5.5V, TA = -40°C to +85°C, unless otherwise noted.) (Note 8)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Fast mode 100 400

SCL Clock Frequency (Note 9) fSCL Standard mode 0 100 kHz

Fast mode 1.3 Bus Free Time Between STOP and

START Conditions tBUF Standard mode 4.7 μs

Fast mode 0.6 Hold Time (repeated) START Condition

(Note 10) tHD:STA Standard mode 4.0 μs

Fast mode 1.3

Low Period of SCL Clock tLOW Standard mode 4.7 μs

Fast mode 0.6

High Period of SCL Clock tHIGH Standard mode 4.0 μs

Fast mode 0 0.9

Data Hold Time (Notes 11, 12) tHD:DAT Standard mode 0 0.9 μs

Fast mode 100

Data Setup Time (Note 13) tSU:DAT Standard mode 250 ns

Fast mode 0.6

Start Setup Time tSU:STA Standard mode 4.7 μs

Fast mode 20 +

0.1CBB

300

Rise Time of Both SDA and SCL

Signals (Note 9) tR

Standard mode 20 +

0.1CBB

1000

Fast mode 20 +

0.1CBB

300

Fall Time of Both SDA and SCL Signals

(Note 9) tF

Standard mode 20 +

0.1CBB

300

Fast mode 0.6

Setup Time for STOP Condition tSU:STO Standard mode 4.7 μs

Capacitive Load for Each Bus Line

(Note 7) CBB 400 pF

Pulse Width of Spikes that Must be

Suppressed by the Input Filter (Note 14) TSP Fast mode 30 ns

Watchdog Strobe (WDS) Pulse Width tWDS 100 ns

Oscillator Stop Flag (OSF) Delay

(Note 8) tOSF 100 ms

Note 1: All voltages are referenced to ground.

Note 2: SCL and WDS only.

Note 3: SDA and SQW/INT.

Note 4: Limits at -40°C are guaranteed by design and not production tested.

Note 5: ICCA—SCL clocking at max frequency = 400kHz. WDS inactive.

Note 6: Specified with WDS input and I2C bus inactive, SCL = SDA = VCC.

Note 7: Measured with a 32.768kHz crystal attached to the X1 and X2 pins.

Note 8: The parameter tOSF is the period of time the oscillator must be stopped in order for the OSF flag to be set over the voltage range of 1.3V

≤ VCC ≤ VCCMAX.

Note 9: A fast mode device can be used in a standard mode system, but the requirement tSU:DAT ≥ to 250ns must then be met. This is

automatically the case if the device does not stretch the LOW period of the SCL signal. If such a device does stretch the LOW period of

the SCL signal, it must output the next data bit to the SDA line tR MAX + tSU:DAT = 1000 + 250 = 1250ns before the SCL line is released.

Note 10: After this period, the first clock pulse is generated.

Note 11: A device must internally provide a hold time of at least 300ns for the SDA signal (referred to the VIHMIN of the SCL signal) in order to

bridge the undefined region of the falling edge of SCL.

Note 12: The maximum tHD:DAT has only to be met if the device does not stretch the LOW period (tLOW) of the SCL signal.

Note 13: CB—total capacitance of one bus line in pF. B

Note 14: This parameter is not production tested.

OSCILLATOR FREQUENCY vs. VCC

DS1371 toc06

VCC (V)

FREQUENCY (Hz)

5.34.84.33.83.32.82.31.8

32767.61

32767.66

32767.71

32767.76

3.767.56

1.3

IOSC0 vs. WDS FREQUENCY

DS1371 toc05

WDS FREQUENCY (kHz)

SUPPLY CURRENT (µA)

800600400200

0 1000

ICCA vs. VCC

SQUARE-WAVE ON

DS1371 toc04

TEMPERATURE ( C)

SUPPLY CURRENT (µA)

806040200-20-40

IOSC0 vs. TEMPERATURE

VCC = 3.3V

DS1371 toc03

TEMPERATURE ( C)

SUPPLY CURRENT (nA)

806040200-20

550

600

650

700

750

500

-40

IOSC1 vs. VCC

SQUARE-WAVE ON

DS1371 toc02

VCC (V)

SUPPLY CURRENT (nA)

5.04.53.5 4.02.5 3.02.0

450

500

550

600

650

700

750

800

850

900

950

400

1.5 5.5

IOSCO vs. VCC

SQUARE-WAVE OFF

DS1371 toc01

VCC (V)

SUPPLY CURRENT (nA)

5.04.54.03.53.02.52.0

350

400

450

500

550

600

300

1.5 5.5

DS1371

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Typical Operating Characteristics

(VCC = 3.3V, TA = +25°C, unless otherwise noted.)

DS1371

Figure 1. Timing Diagram

Power

GND

Oscillator

Interface

SDA

SCL

32-Bit

Counter

Alarm/

Watchdog

Stat/Ctrl

X1 M

24-Bit

Counter

WDS

÷4 ÷4096

÷4096 1Hz

CLR

8192Hz

4096Hz

1Hz

4096Hz

32,768Hz

÷2

SQW

INT

SQW/

WACE

WD/

INTCN

DS1371

Figure 2. Functional Diagram

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DS1371

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PIN DESCRIPTION

PIN NAME FUNCTION

1, 2 X1, X2

These signals are connections for a standard 32.768kHz quartz crystal. The internal

oscillator circuitry is designed for operation with a crystal having a specified load

capacitance (CL) of 6pF. No external resistors or capacitors are required. For more

information about crystal selection and crystal layout considerations, refer to

Application Note 58: Crystal Considerations with Dallas Real-Time Clocks. The

DS1371 can also be driven by an external 32.768kHz oscillator. In this configuration,

the X1 pin is connected to the external oscillator signal and the X2 pin is floated.

3 WDS

Watchdog Input. A positive edge-triggered hardware interrupt input that restarts the

watchdog counter when this signal transitions from a low to a high. While WDS remains

at a static low or high, the watchdog counter continues to decrement.

4 GND Ground

5 SDA I2C Serial Data. Input/output for I2C data.

6 SCL I2C Serial Clock. Input for I2C clock.

7 SQW/INT Square-Wave/Interrupt Output. This pin is used to output the programmable square-

wave or alarm interrupt signal. It is open drain and requires an external pullup resistor.

8 VCC Supply Voltage Terminal

Detailed Description

The DS1371 is a real-time clock (RTC) with a I2C serial interface that provides elapsed seconds from a

user-defined starting point in a 32-bit counter (Figure 2). A 24-bit counter can be configured as either a

watchdog counter or as an alarm counter. An on-chip oscillator circuit uses a customer-supplied

32.768kHz crystal to keep time.

Oscillator Circuit

The DS1371 uses an external 32.768kHz crystal. The oscillator circuit does not require any external

resistors or capacitors to operate (Figure 2). Table 1 specifies several crystal parameters for the external

crystal. Using a crystal with the specified characteristics, the startup time is usually less than one second.

Clock Accuracy

The accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match

between the capacitive load of the oscillator circuit and the capacitive load for which the crystal was

trimmed. Additional error is added by crystal frequency drift caused by temperature shifts. External

circuit noise coupled into the oscillator circuit can result in the clock running fast. Figure 3 shows a

typical PC board layout for isolation of the crystal and oscillator from noise. Refer to Application Note

58: Crystal Considerations with Dallas Real-Time Clocks for detailed information.

DS1371

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Table 1. Crystal Specifications*

PARAMETER SYMBOL

MIN TYP MAX UNITS

Nominal Frequency fO 32.768 kHz

Series Resistance ESR 50 kΩ

Load Capacitance CL 6 pF

*The crystal, traces, and crystal input pins should be isolated from RF generating signals. Refer to Application Note 58: Crystal Considerations

for Dallas Real-Time Clocks for additional specifications.

LOCAL GROUND PLANE (LAYER 2)

CRYSTAL

GND

Figure 3. Layout Example

DS1371

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Address Map

Table 2 shows the address map for the registers of the DS1371. During a multibyte access, when the

address pointer reaches the end of the register space (08h), it wraps around to location 00h. On an I2C

START, STOP, or address pointer incrementing to location 00h, the current time is transferred to a

second set of registers. The time information is read from these secondary registers, while the clock may

continue to run. This eliminates the need to reread the registers in case of an update of the main registers

during a read.

Table 2. Address Map

ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 FUNCTION

00H TOD COUNTER BYTE 0 Time-of-Day

Counter

01H TOD COUNTER BYTE 1 Time-of-Day

Counter

02H TOD COUNTER BYTE 2 Time-of-Day

Counter

03H TOD COUNTER BYTE 3 Time-of-Day

Counter

04H WD/ALM COUNTER BYTE 0 Watchdog/

Alarm Counter

05H WD/ALM COUNTER BYTE 1 Watchdog/

Alarm Counter

06H WD/ALM COUNTER BYTE 2 Watchdog/

Alarm Counter

07H EOSC WACE WD/ALM 0 INTCN RS2 RS1 AIE Control

08H OSF 0 0 0 0 0 0 AF Status

Note: Unless otherwise specified, the state of the registers are not defined when power is first applied.

DS1371

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Time-of-Day Counter

The time-of-day counter is a 32-bit up counter. The contents can be read or written by accessing the

address range 00h–03h. When the counter is read, the current time of day is latched into a register, which

is output on the serial data line while the counter continues to increment. Writing to the counter resets the

countdown chain for the time-of-day counter (Figure 2). The watchdog countdown chain is unaffected. If

the square-wave output is enabled and is set to 1Hz, the output resets when the countdown chain is reset.

Because the other square-wave frequencies are derived before the section of the countdown chain that is

reset, the other frequencies are unaffected by a write to the time-of-day counter.

Watchdog/Alarm Counter

If the counter is not needed, it can be disabled and used as a 24-bit cache of NV RAM by setting the

WACE bit in the control register to logic 0. If all 24 bits of the watchdog/alarm counter are written to

zero, the counter is disabled, independent of the WACE bit setting. When the watchdog counter is written

to a nonzero value, and WACE is written to logic 1, the function of the counter is determined by the

WD/ALM bit.

Note: The WDS input must be low when writing to the watchdog counter registers.

When the WD/ALM bit in the control register is set to a logic 0, the WD/ALM counter decrements every

second until it reaches zero. At this point, the AF bit in the status register is set to a 1 and the counter is

reloaded and restarted. AF remains set until cleared by writing it to a 0. If INTCN = AIE = 1, the

SQW/INT pin will go active whenever AF = 1.

Note: WACE must be set to a logic 1 after the alarm value is written.

When the WD/ALM bit is set to logic 1, the WD/ALM counter decrements every 1/4096 of a second

(approximately every 244μs) until it reaches zero. When any of the watchdog counters bytes are read, the

seed value is reloaded and the counter restarts. Writing to the watchdog counter updates the seed value

and reloads the counter with the new seed value. A low to high transition on the WDS input reloads and

restarts the counter with the seed value. When the counter reaches zero, the AF bit is set and the counter

stops. The AF bit remains set until cleared by writing it to 0. If INTCN and AIE are both at logic 1 when

the AF bit becomes set, the SQW/INT pin pulses low for 250ms. At the end of the 250ms pulse, the AF

bit is cleared and SQW/INT becomes high impedance.

Note: WACE must be toggled from a logic 0 to a logic 1 after the watchdog counter is written from a

zero to a nonzero value.

The 250ms pulse on SQW/INT cannot be truncated by writing either AF or AIE to zero during the low

time. If the WD/ALM counter is written during the 250ms pulse, the counter starts decrementing upon the

pulse completion.

DS1371

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Special Purpose Registers

The DS1371 has two additional registers (07h–08h) that control the WD/ALM counter, square-wave

output, and interrupts.

Control Register (07h)

Bit # 7 6 5 4 3 2 1 0

Name EOSC WACE WD/ALM 0 INTCN RS2 RS1 AIE

Default 0 0 0 0 0 1 1 0

Bit 7: Enable Oscillator (EOSC). When set to logic 0, the oscillator is started. When set to logic 1, the

oscillator is stopped. When this bit is set to a logic 1, the oscillator is stopped and the DS1371 is placed

into a low-power standby mode (IDDR). This bit is clear (logic 0) when power is first applied.

Bit 6: WD/ALM Counter Enable (WACE). When set to logic 1, the WD/ALM counter is enabled.

When set to logic 0, the WD/ALM counter is disabled, and the 24-bits can be used as general-purpose

RAM. This bit is clear (logic 0) when power is first applied.

Bit 5: WD/ALM Counter Select (WD/ALM). When set to logic 0, the counter decrements every second

until it reaches 0 and is then reloaded and restarted. When set to logic 1, the WD/ALM counter

decrements every 1/4096 of a second (approximately every 244μs) until it reaches 0, sets the AF bit in the

status register, and stops. If any of the WD/ALM counter registers are read or written, or a rising edge on

the WDS pin occurs before the counter reaches 0, the counter is reloaded and restarted. This bit is clear

(logic 0) when power is first applied.

Bit 3: Interrupt Control (INTCN). This bit controls the SQW/INT signal. When the INTCN bit is set to

logic 0, a square wave is output on the SQW/INT pin whose frequency is defined by bits RS2 and RS1.

The oscillator must also be enabled for the square wave to be output. When the INTCN bit is set to logic

1, then this permits the alarm flag bit in the status register to assert SQW/INT (provided that the alarm is

also enabled). The alarm flag is always set, regardless of the state of the INTCN bit. The INTCN bit is set

to logic 0 when power is first applied.

Bits 2 and 1: Rate Select 1 and 2 (RS2 and RS1). These bits control the frequency of the square-wave

output when the square wave has been enabled. Table 3 shows the square-wave frequencies that can be

selected with the RS bits. These bits are both set (logic 1) when power is first applied.

Bit 0: Alarm Interrupt Enable (AIE). When set to logic 1, this bit permits the AF bit in the status

does not initiate the SQW/INT signal. If the WD/ALM bit is set to a logic 1 and the AF flag is set, writing

AIE to a 0 does not truncate the 250ms pulse on the SQW/INT pin. The AIE bit is at logic 0 when power

is first applied.

Table 3. SQW/INT Operating Modes

WACE WD/ALM INTCN AIE RS2 RS1 SQW/INT OUTPUT

X X 0 X 0 0 1Hz

X X 0 X 0 1 4.096kHz

X X 0 X 1 0 8.192kHz

X X 0 X 1 1 32.768kHz

1 0 1 1 X X Alarm

1 1 1 1 X X WD

DS1371

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Status Register (08h)

Bit # 7 6 5 4 3 2 1 0

Name OSF 0 0 0 0 0 0 AF

Default 1 0 0 0 0 0 0 —

Bit 7: Oscillator Stop Flag (OSF). A logic 1 in this bit indicates that the oscillator either is stopped or

was stopped for some period and can be used to judge the validity of the timekeeping data. This bit is set

to logic 1 any time that the oscillator stops. The following are examples of conditions that can cause the

OSF bit to be set:

• The first time power is applied.

• The voltage present on VCC is insufficient to support oscillation.

• The EOSC bit is turned off.

• External influences on the crystal (e.g., noise, leakage, etc.)

• This bit remains at logic 1 until written to logic 0.

Bit 0: Alarm Flag (AF). A logic 1 in the AF bit indicates that the WD/ALM counter reached 0. If

INTCN is set to a 1, and WD/ALM is set to 0 and AIE is set to 1, the SQW/INT pin goes low and stays

low until AF is cleared. AF is cleared when written to logic 0. This bit can only be written to logic 0.

Attempting to write logic 1 leaves the value unchanged. If INTCN and WD/ALM are set to 1 and the AIE

is set to 1, the SQW/INT pin pulses low for 250ms when the WD/ALM counter reaches 0 and sets AF =

1. At the completion of the 250ms pulse, the DS1371 clears the AF bit to a 0. If the 250ms pulse is active,

writing AF to a 0 does not truncate the pulse.

I2C Serial Interface

The DS1371 supports a bidirectional I2C bus and data transmission protocol. A device that sends data

onto the bus is defined as a transmitter and a device receiving data as a receiver. The device that controls

the message is called a “master.” The devices that are controlled by the master are “slaves.” The bus must

be controlled by a master device that generates the serial clock (SCL), controls the bus access, and

generates the START and STOP conditions. The DS1371 operates as a slave on the I2C bus. Within the

I2C bus specifications a standard mode (100kHz clock rate) and a fast mode (400kHz clock rate) are

defined. The DS1371 works in both modes. Connections to the bus are made through the open-drain I/O

lines SDA and SCL.

The following bus protocol has been defined (Figure 4):

• Data transfer can be initiated only when the bus is not busy.

• During data transfer, the data line must remain stable whenever the clock line is HIGH. Changes in

the data line while the clock line is high are interpreted as control signals.

Accordingly, the following bus conditions have been defined:

Bus not busy: Both data and clock lines remain HIGH.

Start data transfer: A change in the state of the data line from high to low, while the clock line is

high, defines a START condition.

Stop data transfer: A change in the state of the data line from low to high, while the clock line is

high, defines a STOP condition.

DS1371

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Data valid: The state of the data line represents valid data when, after a START condition, the

data line is stable for the duration of the high period of the clock signal. The data on the line must

be changed during the low period of the clock signal. There is one clock pulse per bit of data.

Each data transfer is initiated with a START condition and terminated with a STOP condition.

The number of data bytes transferred between the START and the STOP conditions is not limited,

and is determined by the master device. The information is transferred byte-wise and each

receiver acknowledges with a ninth bit. Within the I2C bus specifications a standard mode

(100kHz clock rate) and a fast mode (400kHz clock rate) are defined.

Acknowledge: Each receiving device, when addressed, is obliged to generate an acknowledge

after the reception of each byte. The master device must generate an extra clock pulse, which is

associated with this acknowledge bit.

A device that acknowledges must pull down the SDA line during the acknowledge clock pulse in

such a way that the SDA line is stable LOW during the HIGH period of the acknowledge-related

clock pulse. Setup and hold times must be taken into account. A master must signal an end of data

to the slave by not generating an acknowledge bit on the last byte that has been clocked out of the

slave. In this case, the slave must leave the data line HIGH to enable the master to generate the

STOP condition.

Figure 4. I2C Data Transfer Overview

DS1371

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Figures 5 and 6 detail how data transfer is accomplished on the I2C bus. Depending upon the state of the

R/W bit, two types of data transfer are possible:

Data transfer from a master transmitter to a slave receiver. The first byte transmitted by the

master is the slave address. Next follows a number of data bytes. The slave returns an

acknowledge bit after each received byte.

Data transfer from a slave transmitter to a master receiver. The first byte (the slave address)

is transmitted by the master. The slave then returns an acknowledge bit. Next follows a number of

data bytes transmitted by the slave to the master. The master returns an acknowledge bit after all

received bytes other than the last byte. At the end of the last received byte, a “not acknowledge” is

returned.

The master device generates all of the serial clock pulses and the START and STOP conditions. A

transfer is ended with a STOP condition or with a repeated START condition. Since a repeated

START condition is also the beginning of the next serial transfer, the bus is not released.

The DS1371 can operate in the following two modes:

Slave receiver mode (DS1371 write mode). Serial data and clock are received through SDA and

SCL. After each byte is received, an acknowledge bit is transmitted. START and STOP conditions

are recognized as the beginning and end of a serial transfer. Address recognition is performed by

hardware after reception of the slave address and direction bit. The slave address byte is the first

byte received after the START condition is generated by the master. The slave address byte

contains the 7-bit DS1371 address, which is 1101000, followed by the direction bit (R/W), which

for a write is a 0. After receiving and decoding the slave address byte the DS1371 outputs an

acknowledge on SDA. After the DS1371 acknowledges the slave address + write bit, the master

transmits a word address to the DS1371. This sets the register pointer on the DS1371, with the

DS1371 acknowledging the transfer. The master may then transmit zero or more bytes of data,

with the DS1371 acknowledging each byte received. The register pointer increments after each

byte is transferred. The master generates a STOP condition to terminate the data write.

Slave transmitter mode (DS1371 read mode). The first byte is received and handled as in the

slave receiver mode. However, in this mode, the direction bit indicates that the transfer direction is

reversed. Serial data is transmitted on SDA by the DS1371 while the serial clock is input on SCL.

START and STOP conditions are recognized as the beginning and end of a serial transfer.

Address recognition is performed by hardware after reception of the slave address and direction

bit. The slave address byte is the first byte received after the START condition is generated by the

master. The slave address byte contains the 7-bit DS1371 address, which is 1101000, followed by

the direction bit (R/W), which for a read is a 1. After receiving and decoding the slave address

byte, the DS1371 outputs an acknowledge on SDA. The DS1371 then begins to transmit data

starting with the register address pointed to by the register pointer. If the register pointer is not

written to before the initiation of a read mode the first address that is read is the last one stored in

the register pointer. The DS1371 must receive a “not acknowledge” to end a read.

DS1371

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...AXXXXXXXXA

1101000

S 0 XXXXXXXX AXXXXXXXX AXXXXXXXX A P

B - Block Select

S - Start

A - Acknowledge (ACK)

P - Stop

<RW>

DATA TRANSFERRED

(X+1 BYTES + ACKNOWLEDGE)

Master to slave

Slave to master

Figure 5. I2C Write Protocol

AXXXXXXXXA

1101000

S 1 XXXXXXXX AXXXXXXXX XXXXXXXX A P

B - Block Select

S - Start

A - Acknowledge (ACK)

P - STOP

A - Not Acknowledge (NACK)

<RW>

DATA TRANSF ERRED

(X+1 BYTES + ACK NOWLEDGE); NOTE: LAST DATA BYTE IS

FOLLOWED BY A NOT ACKNOWLEDGE (A) SIGNAL)

Master to slave

Slave to master

...A

Figure 6. I2C Read Protocol

AXXXXXXXX

1101000

XXXXXXXX AXXXXXXXX XXXXXXXX A P

B - Block Select

S - Start

Sr - Repeated Start

A - Acknowledge (ACK)

P - Stop

A - Not Acknowledge (NACK)

<RW>

DATA TRANSF ERRED

(X+1 BYTES + ACKNOWLEDGE); NOTE: LAST DATA BYTE IS

FOLLOWED BY A NOT ACKNOWLEDGE (A) SIGNAL)

Master to slave

Slave to master

...

AXXXXXXXXA0

1101000

Sr A1

<Data(n)> <Data(n+1)> <Data(n+2)> <Data(n+X)>

<RW>

Figure 7. I2C Data Read (Write Pointer, Then Read ) Protocol

Chip Information

TRANSISTOR COUNT: 11,036

PROCESS: CMOS

SUBSTRATE CONNECTED TO GROUND

Thermal Information

Theta-JA: 221°C/W

Theta-JC: 39°C/W

Package Information

For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.

PACKAGE DOCUMENT NUMBER

8-pin μSOP 21-0036

DS1371

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Maxim/Dallas Semiconductor cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim/Dallas Semiconductor product.

No circuit patent licenses are implied. Maxim/Dallas Semiconductor reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

The Maxim logo is a registered trademark of Maxim Integrated Products, Inc. The Dallas logo is a registered trademark of Dallas Semiconductor Corporation.

Revision History

REV DATE DESCRIPTION

110502 Initial data sheet release.

051203 (Page 14) In Figures 6 and 7, corrected the slave address and removed the second

“START.”

061406

Changed all 2-wire references to I2C.

(Page 1) Added lead-free packages to the Ordering Information table.

(Page 2) Removed “A” from J-STD-020 (Soldering Tem perature) reference.

Removed Figure 3 (oscillator circuit) and incorporated into new Figure 2 (page 5).

(Page 6) In Pin Description table, added sentence saying no external resistors or

capacitors are required for pins 1 and 2 (X1 and X2).

(Page 7) Removed guard ring from Figure 3 (formerly Figure 4).

(Page 9) Updated the Watchdog/Alarm Counter section.

(Page 10) In Table 3, added the control bits affecting SQW/INT output operation.

(Page 11) In the I2C Serial Interface section (formerly 2-Wire Serial Interface), added text

about the part working in fast and standard I2C modes.

(Page 14) Added package drawing information table.

022207

(Page 1) Corrected top mark information in the Ordering Information table.

(Page 2) Changed IDDR max from 50nA to 100nA.

(Page 7) In Table 1, changed ESR max from 45kΩ to 50kΩ.

(Page 8) In Table 2, changed WD/ALM to WD/ALM for address 07h (Control Register).

070607

(Page 2) Added “noncondensing” to Operating Temperature Range requirement in the

Absolute Maximum Ratings section.

(Page 14) Corrected/added I2C read and write protocol figures.

(Page 14) Changed package information document number to 21-0036.