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DS1629
Digital Thermometer and Real-Time Clock/Calendar
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 to 5.5V) Applications Include PCs/PDAs, Cellular Telephones, Office Equipment, Data Loggers, or Any Thermally Sensitive System 8-Pin (150-mil) SO Package
PIN CONFIGURATION PIN DESCRIPTION SDA - 2-Wire Serial Data Input/Output SCL - 2-Wire Serial Clock GND - Ground ALRM - Thermostat and Clock Alarm Output X1 - 32.768kHz Crystal Input X2 - 32.768kHz Crystal Feedback Output OSC - Buffered Oscillator Output VDD - Power-Supply Voltage (+2.2V to +5V)
DESCRIPTION The DS1629 2-wire digital thermometer and real-time clock (RTC) integrates the critical functions of a real-time clock and a temperature monitor in a small outline 8-pin SO 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.
DS1629 2-Wire Digital Thermometer and Real-Time Clock GND
ALRM
SCL
SDA VDD
OSC
X1
X2
SO (150 mils)
DS1629
The open-drain alarm output of the DS1629 will become active when either the measured temperature exceeds the programmed overtemperature 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 data logging, the DS1629 features 32 bytes of SRAM. Applications for the DS1629 include personal computers/PDAs, cellular telephones, office equipment, thermal data loggers, or any microprocessor-based, thermally-sensitive system.
ORDERING INFORMATION PART TOP MARK PIN-PACKAGE DS1629S+ DS1629 8 SO (150 mils) DS1629S+T&R DS1629 8 SO (150 mils) (2500 piece) +Denotes a lead(Pb)-free/RoHS-compliant package. T&R = Tape and reel.
DETAILED PIN DESCRIPTION Table 1 PIN NAME FUNCTION 1 SDA Data Input/Output Pin for 2-Wire Serial Communication Port 2 SCL Clock Input/Output Pin for 2-Wire Serial Communication Port ALRM Alarm Output. Open drain time/temperature alarm output with configurable active state. 4 GND Ground 5 X2 32.768kHz Feedback Output 6 X1 32.768kHz Crystal Input 7 OSC Oscillator Output. Open-drain output used for microcontroller clock input. 8 VDD Supply Voltage. 2.2V to 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 and clock alarm comparators 6. Oscillator divider and 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.
DS1629
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 32.768kHz 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. 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 data logging, 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.
DS1629
BLOCK DIAGRAM Figure 1 DS1629
OPERATION—MEASURING TEMPERATURE The DS1629 measures temperature using a bandgap-based temperature sensor. A delta-sigma analog-to-digital converter (ADC) converts the measured temperature to a digital value that is calibrated in °C; for °F applications, a lookup table or conversion routine must be used. 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. The very first time the DS1629 is powered up from the factory, it begins temperature conversions and performs conversions 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/Status Register section. The temperature reading is provided in a 9-bit, two’s complement format. Table 2 describes the exact relationship of output data to measured temperature data. The data is transmitted through the 2-wire serial interface, MSB first. The DS1629 can measure temperature over the range of -55°C to +125°C in 0.5°C increments. 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 reading the temperature and truncating the 0.5°C bit (the LSB) from the read value. This value is TEMP_READ. A Read Counter (A8h) command should be issued to yield the 8-bit COUNT_REMAIN value. The Read Slope (A9h) command should then be issued to obtain the 8-bit COUNT_PER_C value. The higher resolution temperature may then be calculated by the user using the following equation:
T = TEMP_READ -0.25 + CCOUNT_PER_
IN)COUNT_REMA- _C(COUNT_PER
Temperature/Data Relationships Table 2 S 26 25 24 23 22 21 20 MSB MSb (unit = °C) LSb 2-1 0 0 0 0 0 0 0 LSB
TEMPERATURE DIGITAL OUTPUT (Binary) DIGITAL OUTPUT (Hex) +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
DS1629
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). See 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 binary-coded 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 24-hour 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 DS1629
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) See the Operation—Configuration/Status Register 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. See the Thermometer Alarm and Clock Alarm sections on how respective alarms are cleared.
DS1629 ALARM TRANSFER FUNCTION Figure 3 DS1629
Thermometer Alarm The thermostat comparator updates as soon as a temperature conversion is complete. When the DS1629’s temperature meets or exceeds the value stored in the high temperature trip register (TH), the TAF flag becomes active (high), and will stay active until the temperature falls below the temperature stored in the low temperature trigger register (TL). The respective register can be accessed over the 2-wire bus via the Access TH (A1h) or Access TL (A2h) commands. Reading from or writing to the respective register is controlled by the state of the R/W bit in the 2-wire control byte (see the 2-Wire Serial Data Bus section). The format of the TH and TL registers is identical to that of the Thermometer register; that is, 9-bit two’s complement representation of the temperature in °C. Both TH and TL are nonvolatile EEPROM registers guaranteed to 2K write cycles.
Thermostat Setpoint (TH/TL) Format Table 3 S 26 25 24 23 22 21 20 MSB MSb (unit = °C) LSb 2-1 0 0 0 0 0 0 0 LSB
Clock Alarm The clock alarm flag (CAF) becomes active within one second after the second, minute, hour, and day (of the week) of the clock register match the respective bytes in the clock alarm register. CAF will remain active until the bus master writes to or reads from either the clock register via the C0h command or the clock alarm register via the C7h command. The format of the clock alarm register is shown in Figure 4. The power-up default of the DS1629 has the clock alarm set to 12:00AM on Sunday. The register can be accessed over the 2-wire bus via the Access Clock Alarm (C7h) command. Reading from or writing to the register is controlled by the state of the R/W bit in the 2-wire control byte (see the 2-Wire Serial Data Bus section). The master must take precaution in programming bit 5 of byte 02h to ensure that the alarm setting matches the current clock mode. Bits designated with a 0 are a don’t care on writes, but will always read out as a 0.
OPERATION—USER SRAM The DS1629 has memory reserved for any purpose the user intends. The page is organized as 32 bytewide locations. The SRAM space is formatted as shown in Table 4. It is accessed via the 2-wire protocol 17h. If the R/W bit of the control byte is set to 1, the SRAM will be read and a 0 in this location allows the master to write to the array. Reads or writes can be performed in the single byte or page mode. As such, the master must write the byte address of the first data location to be accessed. If the bus master is writing to/reading from the SRAM array in the page mode (multiple byte mode), the address pointer will automatically wrap from address 1Fh to 00h following the ACK after byte 1Fh. The SRAM array does not have a defined power-up default state. See the Command Set section for details
DS1629
SRAM FORMAT Table 4 BYTE CONTENTS 00h SRAM BYTE 0 01h SRAM BYTE 1 02h SRAM BYTE 2 . . . . . . 1Eh SRAM BYTE 30 1Fh SRAM BYTE 31
CLOCK ALARM REGISTER FORMAT Figure 4 OPERATION—CONFIGURATION/STATUS REGISTER The configuration/status register is accessed via the Access Config (ACh) function command. Writing to or reading from the register is determined by the R/W bit of the 2-wire control byte (see the 2-Wire Serial Data Bus section). Data is read from or written to the configuration register MSb first. The format of the register is illustrated in Figure 5. The effect each bit has on DS1629 functionality is described along with the power-up state and volatility. The user has read/write access to the MSB and read-only access to the LSB of the register.
Configuration/Status Register Figure 5 OS1 OS0 A1 A0 0 CNV POL 1SH MSB MSb LSb CAF TAF CAL TAL 0 0 0 0 LSB
1SH = Temperature Conversion Mode. If 1SHOT is 1, the DS1629 will perform one temperature conversion upon reception of the Start Convert T protocol. If 1SHOT is 0, the DS1629 will continuously perform temperature conversions and store the last completed result in the Thermometer Register. The user has read/ write access to the nonvolatile bit, and the factory default state is 0 (continuous mode).
POL = ALRM Polarity Bit. If POL = 1, the active state of the ALRM output will be high. A 0 stored in this location sets the thermostat output to an active-low state. The user has read/write access to the nonvolatile POL bit, and the factory default state is 0 (active low).
CNV = Power-up conversion state. If CNV = 0 (factory default), the DS1629 will automatically initiate a temperature conversion upon power-up and supply stability. Setting CNV = 1 causes the DS1629 to power up in a standby state. Table 5 illustrates how the user can set 1SH and CNV, depending on the power consumption sensitivity of the application.
DS1629
Thermometer Power-Up Modes Table 5 CNV ISH MODE 0 0 Powers up converting continuously (factory default) 1 Automatically performs one conversion upon power-up. Subsequent conversions require a Start Convert T command. 0 Powers up in standby; upon Start Convert T command, conversions will be performed continuously. 1 Powers up in standby; upon Start Convert T command, a single conversion will be performed and stored.
A0, A1 = Alarm Mode. Table 6 defines the DS1629 alarm mode, based on the settings of the A0 and A1 bits. These bits define what event will activate the ALRM output. The alarm flags—CAF, TAF, CAL, TAL—are functional regardless of the state of these bits. Both locations are read/write and nonvolatile, and the factory default state disables the ALRM output (A0 = A1 = 0).
Alarm Mode Configuration Table 6 A1 A0 ALARM MODE 0 0 Neither Thermal or Time (Disabled) 0 1 Thermal Only 1 0 Time Only 1 1 Either Thermal or Time
OS0, OS1 = Oscillator Output Setting. Table 7 defines the frequency of the OSC output, as defined by the settings of these bits. Both locations are read/write and nonvolatile, and the factory default state sets the OSC frequency equal to the crystal frequency (OS0 = OS1 = 1). The output should be disabled if the user does not intend to use it to reduce power consumption.
OSC Frequency Configuration Table 7 OS1 OS0 OSC FREQUENCY 0 0 Disabled 0 1 1/8fO 1 0 1/4fO 1 1 fO
CAF = Clock Alarm Flag. This volatile status bit will be set to 1 when the clock comparator is in an active state. Once set, it will remain 1 until reset by writing to or reading from either the clock register or clock alarm register. A 0 in this location indicates the clock is not in an alarm condition. This is a read-only bit (writes to this location constitute a don’t care) and the power-up default is the flag cleared (CAF = 0).
TAF = Thermal Alarm Flag. This volatile status bit will be set to 1 when the thermal comparator is in an active state. Once set, it will remain 1 until measured temperature falls below the programmed TL setting. A 0 in this location indicates the thermometer is not in an alarm condition. This is a read-only bit (writes to this location constitute a don’t care) and the power-up default is the flag cleared (TAF = 0).
DS1629
CAL = Clock Alarm Latch. This volatile status bit will be set to 1 when the clock comparator becomes active. Once set, it will remain latched until DS1629 power is cycled. A 0 in this location indicates the clock has never been in an alarm condition since the DS1629 was powered-up. This is a read-only bit (writes to this location constitute a don’t care) and the power-up default is the flag cleared (CAL = 0).
TAL = Thermal Alarm Latch. This volatile status bit will be set to 1 when the thermal comparator becomes active. Once set, it will remain latched until DS1629 power is cycled. A 0 in this location indicates the DS1629 temperature has never exceeded TH since power-up. This is a read-only bit (writes to this location constitute a don’t care) and the power-up default is the flag cleared (TAL = 0).
0 = Don’t care. Don’t care on a write, but will always read out as a 0. 2-WIRE SERIAL DATA BUS The DS1629 supports a bidirectional two-wire 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 which generates the serial clock (SCL), controls the bus access, and generates the START and STOP conditions. The DS1629 operates as a slave on the 2-wire bus. Connections to the bus are made via the open-drain I/O lines SDA and SCL. The following bus protocol has been defined: • Data transfer may 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 will be 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 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 the STOP condition.
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 START and STOP conditions is not limited, and is determined by the master device. The information is transferred byte-wise and each receiver acknowledges with a 9th bit. The maximum clock rate of the DS1629 is 400kHz.
DS1629
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. Of course, 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 6 details how data transfer is accomplished on the two-wire bus. Depending upon the state of the R/W bit, two types of data transfer are possible: 1.
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. 2.
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 will not be released. The DS1629 may operate in the following two modes: 1.
Slave receiver 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. 2.
Slave transmitter mode: The first byte is received and handled as in the slave receiver mode. However, in this mode, the direction bit will indicate that the transfer direction is reversed. Serial data is transmitted on SDA by the DS1629 while the serial clock is input on SCL. START and STOP conditions are recognized as the beginning and end of a serial transfer.
SLAVE ADDRESS A control byte is the first byte received following the START condition from the master device. The control byte consists of a 4-bit control code; for the DS1629, this is set as 1001 binary for read and write operations. The next 3 bits of the control byte are the device select bits (A2, A1, A0). All 3 bits are hard-wired high for the DS1629. Thus, only one DS1629 can reside on a 2-wire bus to avoid contention; however, as many as seven other devices with the 1001 control code can be dropped on the 2-wire bus so long as none contain the 111 address. The last bit of the control byte (R/W) defines the operation to be performed. When set to a 1 a read operation is selected, and when set to a 0 a write operation is selected.
