Rainbow Electronics DS1629 User Manual

DS1629

2-Wire Digital Thermometer

www.dalsemi.com

1234876

and Real Time Clock

FEATURES

§ Measures temperatures from -55°C to

+125°C; Fahrenheit equivalent is -67°F to 257°F

§ Real time clock counts seconds, minutes,

hours, date of the month, month, day of the week, and year with leap year compensation through the year 2100

§ Thermometer accuracy is ±2.0°C (typ)

§ Thermometer resolution is 9 bits (expandable)

§ Thermostatic and time alarm settings are user

definable. Dedicated open-drain Alarm output

§ 32 bytes SRAM for general data storage

§ Data is read from/written to via a 2-wire serial

interface. (open drain I/O lines)

§ Wide power supply range (2.2V - 5.5V)

§ Applications include personal

computers/PDAs, cellular telephones, office equipment, dataloggers, or any thermally sensitive system

§ 8-pin 150mil SOIC package

PIN ASSIGNMENT

SDA V SCL

ALRM

GND

DS1629S 8-Pin SOIC

(150-mil)

OSC X

PIN DESCRIPTION

SDA - 2-Wire Serial Data Input/Output SCL - 2-Wire Serial Clock GND - Ground ALRM - Thermostat & Clock Alarm

Output

OSC - Buffered Oscillator Output V

- 32.768 kHz Crystal Input

- 32.768 kHz Crystal Feedback Output

- Power Supply Voltage (+2.2V to +5V)

DESCRIPTION

The DS1629 2-Wire Digital Thermometer and Real Time Clock integrates the critical functions of a real time clock and a temperature monitor in a small outline 8-pin SOIC package. Communication to the DS1629 is accomplished via a 2-wire interface. The wide power supply range and minimal power requirement of the DS1629 allow for accurate time/temperature measurements in battery-powered applications.

The digital thermometer provides 9-bit temperature readings which indicate the temperature of the device. No additional components are required; the device is truly a “temperature-to-digital” converter. The clock/calendar provides seconds, minutes, hours, day, date of the month, day of the week, month, and year. The end of the month date is automatically adjusted for months with less than 31 days, including corrections for leap years. It operates in either a 12- or 24-hour format with AM/PM indicator in 12-hour mode.The crystal oscillator frequency is internally divided, as specified by device configuration. An open-drain output is provided that can be used as the oscillator input for a microcontroller.

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The open-drain alarm output of the DS1629 will become active when either the measured temperature exceeds the programmed over-temperature limit (TH) or current time reaches the programmed alarm setting. The user can configure which event (time only, temperature only, either, or neither) will generate an alarm condition. For storage of general system data or time/temperature datalogging, the DS1629 features 32 bytes of SRAM. Applications for the DS1629 include personal computers/ PDAs, cellular telephones, office equipment, thermal dataloggers, or any microprocessor-based, thermally-sensitive system.

DETAILED PIN DESCRIPTION Table 1

PIN SYMBOL DESCRIPTION

1 SDA Data input/output pin for 2-wire serial communication port. 2 SCL Clock input/output pin for 2-wire serial communication port. 3 ALRM Alarm output Open drain time/temperature alarm output with configurable active

state 4 GND 5 X 6 X

2 1

7 OSC Oscillator Output. Open-drain output used for microcontroller clock input. 8 V

Ground pin.

32.768 kHz Feedback Output .

32.768 kHz Crystal input.

Supply voltage 2.2V - 5.5V input power pin.

OVERVIEW

A block diagram of the DS1629 is shown in Figure 1. The DS1629 consists of six major components:

1. Direct-to-digital temperature sensor

2. Real time clock

3. 2-wire interface

4. Data registers

5. Thermal & clock alarm comparators

6. Oscillator divider & buffer

The factory-calibrated temperature sensor requires no external components. The very first time the DS1629 is powered up it begins temperature conversions, and performs conversions continuously. The host can periodically read the value in the temperature register, which contains the last completed conversion. As conversions are performed in the background, reading the temperature register does not affect the conversion in progress.

The host can modify DS1629 configuration such that it does not power up in the auto-convert or continuous convert modes. This could be beneficial in power-sensitive applications.

The real time clock/calendar maintains a BCD count of seconds, minutes, hours, day of the week, day of the month, month, and year. It does so with an internal oscillator/ divider and a required 32.768 kHz crystal. The end of the month date is automatically updated for months with less than 31 days, including compensation for leap years through the year 2100. The clock format is configurable as a 12- (power-up default) or 24-hour format, with an AM/PM indicator in the 12-hour mode. The RTC can be shut down by clearing a bit in the clock register.

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The crystal frequency is internally divided by a factor that the user defines. The divided output is buffered and can be used to clock a microcontroller.

The DS1629 features an open-drain alarm output. It can be configured to activate on a thermal event, time event, either thermal or time, or neither thermal nor time (disabled, power-up state). The thermal alarm becomes active when measured temperature is greater than or equal to the value stored in the TH thermostat register. It will remain active until temperature is equal to or less than the value stored in TL, allowing for programmable hysteresis. The clock alarm will activate at the specific minute of the week that is programmed in the clock alarm register. The time alarm is cleared by reading from or writing to either the clock register or the clock alarm register.

The DS1629 configuration register defines several key items of device functionality. It sets the conversion mode of the digital thermometer and what event, if any, will constitute an alarm condition. It also sets the active state of the alarm output. Finally, it enables/disables and sets the division factor for the oscillator output.

The DS1629 also features 32 bytes of SRAM for storage of general information. This memory space has no bearing on thermometer or chronograph operation. Possible uses for this memory are time/temperature histogram storage, thermal datalogging, etc.

Digital data is written to/read from the DS1629 via a 2-wire interface, and all communication is MSb first. Individual registers are accessed by unique 8-bit command protocols.

The DS1629 features a wide power supply range (2.2V ≤ VDD ≤ 5.5V) for clock functionality, SRAM data retention, and 2-wire communication. EEPROM writes and temperature conversions should only be

performed at 2.7V ≤ VDD ≤ 5.5V for reliable results.

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DS1629 FUNCTIONAL BLOCK DIAGRAM Figure 1

DS1629

OPERATION-Measuring Temperature

The DS1629 measures temperature through the use of an on-chip temperature measurement technique with an operating range from -55°C to +125°C. The device can be configured to perform a single conversion, store the result, and return to a standby mode or it can be programmed to convert continuously. Regardless of the mode used, the last completed digital temperature conversion is retrieved from the temperature register using the Read Temperature (AAh) protocol, as described in detail in the “Command Set” section. Details on how to change the settings after power-up are contained in the “OPERATION-Configuration” section.

The DS1629 measures temperature by counting the number of clock cycles that an oscillator with a low temperature coefficient goes through during a gate period determined by a high temperature coefficient

oscillator. The counter is preset with a base count that corresponds to -55°C. If the counter reaches 0 before the gate period is over, the temperature register, which is also preset to the -55°C value, is incremented, indicating that the temperature is higher than -55°C.

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At the same time, the counter is then preset with a value determined by the slope accumulator circuitry. This circuitry is needed to compensate for the parabolic behavior of the oscillators over temperature. The counter is then clocked again until it reaches 0. If the gate period is still not finished, then this process repeats.

The slope accumulator is used to compensate for the nonlinear behavior of the oscillators over temperature, yielding a high resolution temperature measurement. This is done by changing the number of counts necessary for the counter to go through for each incremental degree in temperature. To obtain the desired resolution, therefore, both the value of the counter and the number of counts per degree C (the value of the slope accumulator) at a given temperature must be known.

Internally, this calculation is done inside the DS1629 to provide 0.5°C resolution. Table 2 describes the exact relationship of output data to measured temperature. For Fahrenheit usage, a lookup table or conversion factor must be used.

Note that temperature is represented in the DS1629 in terms of a 0.5°C LSB, yielding the 9-bit format illustrated in Table 2. Higher resolutions may be obtained by implementing the algorithm in Application Note 105 and performing the following calculation. The 8-bit COUNT_REMAIN value can be obtained via the Read Counter (A8h) command and the COUNT_PER_C value (also 8-bit) is read via the Read Slope command (A9h).

T = TEMP_READ -0.25 +

EMAIN)_C_COUNT_R(COUNT_PER

CCOUNT_PER_

Temperature/Data Relationships Table 2

S 2

MSb (unit = °C) LSb

-1

0 0 0 0 0 0 0 LSB

TEMPERATURE

+125°C 01111101 00000000 7D00h

+25°C 00011001 00000000 1900

0.5°C 00000000 10000000 0080 0°C 00000000 00000000 0000

-0.5°C 11111111 10000000 FF80

-25°C 11100111 00000000 E700h

-55°C 11001001 00000000 C900h

DIGITAL OUTPUT

(Binary)

(Hex)

MSB

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OPERATION-Real Time Clock/Calendar

DS1629 real-time clock/calendar data is accessed with the 2-wire command protocol C0h. If the R/W bit in the 2-wire control byte is set to 0, the bus master will set the clock (write to the clock register). The bus master sets the R/W bit to 1 to read the current time (read from the clock register). Refer to the “2-Wire Serial Bus” section for details on this protocol.

The format of the clock register is shown below in Figure 2. Data format for the clock register is binarycoded decimal (BCD). Most of the clock register is self-explanatory, but a few of the bits require elaboration.

CH = Clock halt bit. This bit is set to 0 to enable the oscillator and set to 1 to disable it. If the bit is changed during a write to the clock register, the oscillator will not be started (or stopped) until the bus master issues a STOP pulse. The DS1629 power-up default has the oscillator enabled (CH=0) so that OSC can be used for clocking a microcontroller at power-up.

12/24 = Clock mode bit. This bit is set high when the clock is in the 12-hour mode and set to 0 in the 24hour mode. Bit 5 of byte 02h of the clock register contains the MSb of the hours (1 for hours 20-23) if the clock is in the 24-hour mode. If the clock mode is set to the 12-hour mode, this is the AM/PM bit. In the 12-hour mode, a 0 in this location denotes AM and a 1 denotes PM. When setting the clock, this bit must be written to according to the clock mode used.

Bits in the clock register filled with 0 are a "don't care" on a write, but will always read out as 0.

DS1629 CLOCK REGISTER FORMAT Figure 2

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OPERATION-Alarms

The DS1629 features an open-drain alarm output with a user-definable active state (factory default is active low). By programming the configuration register, the user also defines the event, if any, would generate an alarm condition. The four possibilities are:

• Temperature alarm only

• Time alarm only

• Either temperature or time alarm

• Alarm disabled (power–up default)

Refer to the “OPERATION-Configuration” section for programming protocol.

If the user chooses the alarm mode under which a thermal or time event generates an alarm condition, it is possible that either or both are generating the alarm. There are status bits in the configuration register (TAF, CAF) that define the current state of each alarm. In this way, the master can determine which event generated the alarm. If both events (thermal and time) are in an alarm state, the ALRM output will remain active until both are cleared. ALRM is the logical OR of the TAF and CAF flags if the device is configured for either to trigger the ALRM output. Figure 3 illustrates a possible scenario with this alarm mode. Refer to the “Thermometer Alarm” and “Clock Alarm” sections on how respective alarms are cleared.

DS1629 ALARM TRANSFER FUNCTION Figure 3

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