Rev 1; 1/04 2-Wire Digital Input RTC with Alarm Features The DS1375 digital real-time clock (RTC) is a low-power clock/calendar that does not require a crystal. The device operates from a digital clock input pin at one of four frequencies: 32.768kHz, 8.192kHz, 60Hz, or 50Hz. It maintains seconds, minutes, hours, day, date, month, and year information. The date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with an AM/PM indicator. Two programmable time-of-day/date alarms, a programmable square-wave output, and 16 bytes of SRAM are provided. Address and data are transferred serially through a 2-wire bidirectional bus. ♦ RTC Counts Seconds, Minutes, Hours, Day, Date, Month, and Year with Leap-Year Compensation Valid Up to 2100 ♦ Two Programmable Alarms ♦ Programmable Square-Wave Output ♦ Operates from a 32.768kHz, 8.192kHz, 60Hz, or 50Hz Digital Clock Signal ♦ 16 Bytes of SRAM ♦ Fast (400kHz) 2-Wire Interface ♦ 1.7V to 5.5V Operation Applications RTC Complement to the DS32kHz TCXO Utility Meters Ordering Information Appliances Consumer Electronics PART Automotive DS1375 TEMP RANGE PIN-PACKAGE -40°C to +85°C 6 TDFN TOP MARK DS1375 Pin Configuration Typical Operating Circuit +3V RPU = tr/CB RPU TOP VIEW RPU CLK 1 VCC SCL VBAT CLK SCA SQW/INT 2 CPU DS1375 INT DS1375 5 SCL DS32kHz SQWINT GND 3 GND 6 VCC VCC GND 4 SDA TDFN, EXPOSED PAD 3mm x 3mm x 0.8mm ______________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 DS1375 General Description DS1375 2-Wire Digital Input RTC with Alarm 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 + 0.3V Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range .............................-55°C to +125°C Soldering Temperature .......................................See IPC/JEDEC J-STD-020A Specification 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 may affect device reliability. RECOMMENDED DC OPERATING CONDITIONS (VCC = +1.7V to +5.5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at VCC = 3.3V, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 3.3 5.5 V 5.5 V Supply Voltage VCC (Note 2) 1.7 Timekeeping Voltage VTK (Note 2) 1.3 Input Logic 1 (SDA, SCL) VIH (Note 2) Supply Voltage, Pullup (SQW/INT, CLK) VPULLUP (Notes 2, 3) Input Logic 0 VIL (Notes 2, 4) Input Leakage (SCL, CLK) ILI I/O Leakage (SDA, SQW/INT) ILO SDA Logic 0 Output IOLSDA SQW/INT Logic 0 Output IOLSQW 0.7 x VCC VCC + 0.3 V 5.5 V -0.3 +0.3 VCC V -1 +1 µA -1 +1 µA 3.0 mA 3.0 mA 250 µA VCC > 2V; VOL = 0.4V VCC < 2V; VOL = 0.2 x VCC VCC > 2V; VOL = 0.4V 1.7V < VCC < 2V; VOL = 0.2 x VCC 1.3V < VCC < 1.7V; VOL = 0.2 x VCC Active Supply Current ICCA (Notes 5, 6) 33 150 µA Standby Current ICCS (Notes 6, 7) 150 500 nA Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: 2 Limits at -40°C are guaranteed by design and not production tested. All voltages are referenced to ground. For the CLK pin, input voltages above VCC + 0.3V cause current to flow into the device. The input current must not exceed the current drawn by the circuit that is connected to VCC. Otherwise, current flows out of the DS1375, raising the voltage level on the VCC bus. VIL MIN on the CLK pin can exceed -0.3V as long as the current is limited to less than 1mA. ICCA—SCL clocking at max frequency = 400kHz. CLK pin running at 32,768Hz, rise and fall times at 10ns or less. Specified with 2-wire bus inactive. _____________________________________________________________________ 2-Wire Digital Input RTC with Alarm (VCC = VCCMIN to VCCMAX, TA = -40°C to +85°C, unless otherwise noted.) (Note 1, Figure 1) PARAMETER SYMBOL SCL Clock Frequency fSCL Bus Free Time Between STOP and START Conditions tBUF Hold Time (Repeated) START Condition (Note 8) tHD:STA Low Period of SCL Clock tLOW High Period of SCL Clock tHIGH Data Hold Time (Notes 9, 10) tHD:DAT Data Setup Time (Note 11) tSU:DAT Start Setup Time tSU:STA tR Fall Time of Both SDA and SCL Signals (Note 12) tF Setup Time for STOP Condition tSU:STO Capacitive Load for Each Bus Line (Note 12) CB Pulse Width of Spikes that Must be Suppressed by the Input Filter tSP Note 10: Note 11: Note 12: Fast mode Standard mode MIN TYP MAX 100 400 0 100 Fast mode 1.3 Standard mode 4.7 Fast mode 0.6 Standard mode 4.0 Fast mode 1.3 Standard mode 4.7 Fast mode 0.6 Standard mode 4.0 µs µs 0 0.9 0 0.9 100 Standard mode 250 Fast mode 0.6 Standard mode 4.7 Standard mode Fast mode Standard mode µs 20 + 0.1CB 0.6 Standard mode 4.7 300 1000 300 300 ns ns µs 400 Fast mode µs ns 20 + 0.1CB Fast mode kHz µs Standard mode Fast mode UNITS µs Fast mode Fast mode Rise Time of Both SDA and SCL Signals (Note 12) Note 8: Note 9: CONDITIONS 30 pF ns After this period, the first clock pulse is generated. A device must internally provide a hold time of at least 300ns for the SDA signal (see the VIHMIN of the SCL signal) to bridge the undefined region of the falling edge of SCL. The maximum tHD:DAT is only met if the device does not stretch the low period (tLOW) of the SCL signal. A fast-mode device can be used in a standard-mode system, but the requirement tSU:DAT ≥ 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. CB—total capacitance of one bus line in pF. _____________________________________________________________________ 3 DS1375 AC ELECTRICAL CHARACTERISTICS DS1375 2-Wire Digital Input RTC with Alarm SDA tBUF tSP tHD:STA tLOW tR tF SCL tHD:STA STOP tSU:STA tHIGH tSU:DAT START tSU:STO REPEATED START tHD:DAT Figure 1. Data Transfer on 2-Wire Serial Bus 8192Hz/4096Hz/1024Hz/1Hz CLK SQW/INT MUX/ BUFFER 1Hz DIVIDER ALARM AND CONTROL REGISTERS CONTROL LOGIC DS1375 CLOCK AND CALENDAR REGISTERS SRAM SCL SERIAL BUS INTERFACE AND ADDRESS REGISTER SDA USER BUFFER (7 BYTES) Figure 2. Functional Diagram Typical Operating Characteristics (VCC = +3.3V, TA = +25°C, unless otherwise noted.) ICCS vs. VCC ICCA vs. VCC DS1375 toc02 250 90 80 SUPPLY CURRENT (µA) SUPPlY CURRENT (nA) 100 DS1375 toc01 300 200 150 100 70 60 50 40 30 20 10 50 0 1.7 2.2 2.7 3.2 3.7 4.2 4.7 5.2 1.7 2.2 VCC (V) 4 _____________________________________________________________________ 2.7 3.2 3.7 VCC (V) 4.2 4.7 5.2 2-Wire Digital Input RTC with Alarm ICCS vs. CLK INPUT VOLTAGE ICCS vs. TEMPERATURE VCC = 3.0V 450 400 SUPPLY CURRENT (µA) 130.0 127.5 125.0 122.5 120.0 DS1375 toc04 132.5 SUPPLY CURRENT (nA) 500 DS1375 toc03 135.0 VCC = 5.0V 350 300 250 VCC = 4.0V 200 150 100 117.5 50 0 115.0 -40 -20 0 20 40 60 80 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 CLK VOLTAGE (V) TEMPERATURE (°C) Pin Description PIN NAME FUNCTION 1 CLK 2 SQW/INT 3 GND Ground 4 SDA Serial Data Input/Output. SDA is the data input/output for the 2-wire serial interface. It is open drain and requires an external pullup resistor. 5 SCL Serial Clock Input. SCL is the clock input for the 2-wire serial interface, and is used to synchronize data movement on the serial interface. 6 VCC DC Power for Primary Power Supply Digital Clock Input. This pin must be 32,768Hz, 8192Hz, 60Hz, or 50Hz square wave, 45% to 55% duty cycle. Square-Wave/Interrupt Output. This pin is open drain and requires an external pullup resistor. Detailed Description The DS1375 digital input RTC with alarm is a low-power clock/calendar with two programmable time-of-day alarms and a programmable square-wave output. Address and data are transferred serially through the 2-wire serial interface bus. The clock/calendar provides seconds, minutes, hours, day, date, month, and year information. The date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with an AM/PM indicator. The DS1375 requires an external clock source selectable between 32,768Hz, 8192Hz, 60Hz, or 50Hz for the timekeeping function. Sixteen bytes of SRAM are provided for additional user storage. Operation The DS1375 operates as a slave device on the serial bus. Access is obtained by implementing a START condition and providing a device identification code, followed by data. Subsequent registers can be accessed sequentially until a STOP condition is executed. The functional diagram in Figure 2 shows the main elements of the serial RTC. Address Map Table 1 shows the address map for the timekeeping registers and SRAM. The 16 bytes of SRAM occupy addresses 10–1Fhex. During a multibyte access, when the address pointer reaches the end of the register space (1Fh), it wraps around to location 00h. On a 2-wire START, STOP, or address pointer incrementing _____________________________________________________________________ 5 DS1375 Typical Operating Characteristics (continued) (VCC = +3.3V, TA = +25°C, unless otherwise noted.) DS1375 2-Wire Digital Input RTC with Alarm Table 1. Timekeeping Registers and SRAM ADDRESS BIT 7 FUNCTION RANGE 00h 0 BIT 6 10 Seconds Seconds Seconds 00–59 01h 0 10 Minutes Minutes Minutes 00–59 02h 0 12/24 Hours Hours 1–12 + AM/PM 00–23 03h 0 0 Day 1–7 04h 0 0 Date Date 00–31 05h Century 0 Months Month/ Century 01–12 + Century 06h BIT 5 BIT 4 AM/PM 10 Hours BIT 3 10 Hours 0 0 BIT 0 Day 10 Date 10 Month 0 BIT 1 0 Year Year 00–99 07h A1M1 10 Year 10 Seconds Seconds Alarm 1 Seconds 00–59 08h A1M2 10 Minutes Minutes Alarm 1 Minutes 00–59 Alarm 1 Hours 1–12 + AM/PM 00–23 09h A1M3 12/24 0Ah A1M4 DY/DT 0Bh A2M2 0Ch A2M3 12/24 0Dh A2M4 DY/DT 0Eh ECLK 0Fh 0 0 10h–1Fh B7 B6 AM/PM 10 Hours 10 Hours Hours Day Alarm 1 Day 1–7 Date Alarm 1 Date 1–31 Minutes Alarm 2 Minutes 00–59 Hours Alarm 2 Hours 1–12 + AM/PM 00–23 Day Alarm 2 Day 1–7 10 Date 10 Minutes AM/PM 10 Hours 10 Hours — 10 Date Alarm 2 Date 1–31 RS2 RS1 INTCN A2IE A1IE Control — 0 0 0 0 A2F A1F Control/ Status — B5 B4 B3 B2 B1 B0 SRAM 00–FFH CLKSEL1 CLKSEL0 Date 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 the main registers update during a read. Note: Unless otherwise specified, the state of the registers is not defined when power is first applied. Clock and Calendar The time and calendar information is obtained by reading the appropriate register bytes. Table 1 shows the RTC registers. The time and calendar data are set or initialized by writing the appropriate register bytes. The contents of the time and calendar registers are in the binary-coded decimal (BCD) format. The DS1375 can be run in either 12-hour or 24-hour mode. Bit 6 of the hours register is defined as the 12- or 24-hour mode select bit. When high, the 12-hour mode is selected. In the 12-hour mode, bit 5 is the AM/PM bit with logic high 6 BIT 2 being PM. In the 24-hour mode, bit 5 is the second 10hour bit (20–23 hours). The century bit (bit 7 of the month register) is toggled when the years register overflows from 99 to 00. The day-of-week register increments at midnight. Values that correspond to the day of week are userdefined but must be sequential (i.e., if 1 equals Sunday, then 2 equals Monday, and so on). Illogical time and date entries result in undefined operation. When reading or writing the time and date registers, secondary (user) buffers are used to prevent errors when the internal registers update. When reading the time and date registers, the user buffers are synchronized to the internal registers on any START or STOP and when the register pointer rolls over to zero. The time information is read from these secondary registers, while the clock continues to run. This eliminates the need to reread the registers in case the main registers update during a read. _____________________________________________________________________ 2-Wire Digital Input RTC with Alarm Alarms The DS1375 contains two time-of-day/date alarms. Alarm 1 can be set by writing to registers 07h–0Ah. Alarm 2 can be set by writing to registers 0Bh–0Dh. The alarms can be programmed (by the alarm enable and INTCN bits of the control register) to activate the SQW/INT output on an alarm match condition. Bit 7 of the time-of-day/date alarm registers are mask bits (Table 2). When all the mask bits for each alarm are logic 0, an alarm only occurs when the values in the timekeeping registers match the corresponding values stored in the time-of-day/date alarm registers. The alarms can also be programmed to repeat every second, minute, hour, day, or date. Table 2 shows the possible settings. Configurations not listed in the table result in illogical operation. that register reflects the day of the week or the date of the month. If DY/DT is written to logic 0, the alarm is the result of a match with date of the month. If DY/DT is written to logic 1, the alarm is the result of a match with day of the week. When the RTC register values match alarm register settings, the corresponding alarm flag A1F or A2F bit is set to logic 1. If the corresponding alarm interrupt enable A1IE or A2IE is also set to logic 1, and the INTCN bit is set to logic 1, the alarm condition activates the SQW/INT signal. The match is tested on the onceper-second update of the time and date registers. Special Purpose Registers The DS1375 has two additional registers (control and status) that control the RTC, alarms, and square-wave output. The DY/DT bits (bit 6 of the alarm day/date registers) control whether the alarm value stored in bits 0–5 of Table 2. Alarm Mask Bits DY/DT ALARM 1 REGISTER MASK BITS (BIT 7) ALARM RATE DY/DT ALARM 2 REGISTER MASK BITS (BIT 7) ALARM RATE A2M4 A2M3 A2M2 A1M4 A1M3 A1M2 A1M1 X 1 1 1 1 Alarm once per second X 1 1 1 Alarm once per minute (00 seconds of every min) X 1 1 1 0 Alarm when seconds match X 1 1 0 Alarm when minutes match X 1 0 0 Alarm when hours and minutes match 0 0 0 0 Alarm when date, hours, and minutes match 1 0 0 0 Alarm when day, hours, and minutes match X 1 1 0 0 Alarm when minutes and seconds match X 1 0 0 0 Alarm when hours, minutes, and seconds match 0 0 0 0 0 Alarm when date, hours, minutes, and seconds match 1 0 0 0 0 Alarm when day, hours, minutes, and seconds match _____________________________________________________________________ 7 DS1375 The countdown chain is reset whenever the seconds register is written. Write transfers occur on the acknowledge from the DS1375. Once the countdown chain is reset, to avoid rollover issues the remaining time and date registers must be written within 1 second. The 1Hz square-wave output, if enabled, transitions high 500ms after the seconds data transfer, provided the clock input is already being driven. DS1375 2-Wire Digital Input RTC with Alarm Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ECLK CLKSEL1 CLKSEL0 RS2 RS1 INTCN A2IE A1IE Control Register (0Eh) Bit 7/Enable Clock (ECLK). When ECLK is set to logic 1, the CLK input pin is enabled to clock the internal divider chain and advance the timekeeping registers. When ECLK is set to logic 0, the divider chain is held in reset, and the time is not allowed to advance. To synchronize the DS1375 time to a reference, write the ECLK bit to 0, write the time value, then write ECLK back to 1. Doing so synchronizes the time value to within one period of the CLK pin from the point in the interface protocol where the ECLK bit is written. ECLK is set to logic 1 when power is first applied. Bits 6, 5/Clock Select Bits 1, 0 (CLKSEL1, CLKSEL0). These bits determine how the CLK input pin is divided down to get the 1Hz reference clock for the timekeeping registers (Table 3). The CLKSEL0–1 bits are cleared to logic 0 when power is first applied. Bits 4, 3/Rate Select (RS2 and RS1). These bits control the frequency of the square-wave output when the square wave has been enabled and the CLKSEL0 and CLKSEL1 bits are set to 0. Table 3 shows the squarewave frequencies that can be selected with the RS bits. These bits are set to logic 1 (8.192kHz) when power is first applied. If either CLKSEL0 or CLKSEL1 are logic 1, the 1Hz signal is output. Bit 2/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. When the INTCN bit is set to logic 1, a match between the timekeeping registers and either of the alarm registers activates the SQW/INT (if the alarm is also enabled). The corresponding 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. Bit 1/Alarm 2 Interrupt Enable (A2IE). When set to logic 1, this bit permits the alarm 2 flag (A2F) bit in the status register to assert SQW/INT (when INTCN = 1). When the A2IE bit is set to logic 0 or INTCN is set to logic 0, the A2F bit does not initiate an interrupt signal. The A2IE bit is disabled (logic 0) when power is first applied. Bit 0/Alarm 1 Interrupt Enable (A1IE). When set to logic 1, this bit permits the alarm 1 flag (A1F) bit in the status register to assert SQW/INT (when INTCN = 1). When the A1IE bit is set to logic 0 or INTCN is set to logic 0, the A1F bit does not initiate the SQW/INT signal. The A1IE bit is disabled (logic 0) when power is first applied. Table 3. CLK Input Frequency, Square-Wave Output Frequency 8 INTCN CLKSEL1 CLKSEL0 INPUT FREQUENCY RS2 RS1 SQUARE-WAVE OUTPUT FREQUENCY 1 X X As selected X X N/A (Interrupt) 0 0 0 32,768Hz 0 0 1Hz 0 0 0 32,768Hz 0 1 1.024kHz 0 0 0 32,768Hz 1 0 4.096kHz 0 0 0 32,768Hz 1 1 8.192kHz 0 0 1 8192Hz X X 1Hz 0 1 0 60Hz X X 1Hz 0 1 1 50Hz X X 1Hz _____________________________________________________________________ 2-Wire Digital Input RTC with Alarm Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 0 0 0 0 0 0 A2F A1F The following bus protocol has been defined (Figure 3): • 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 can 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 data line’s state from high to low, while the clock line is high, defines a START condition. Stop data transfer: A change in the data line’s state from low to high, while the clock line is high, defines a STOP condition. Data valid: The data line’s state 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 informa- Status Register (0Fh) Bit 1/Alarm 2 Flag (A2F). A logic 1 in the alarm 2 flag bit indicates that the time matched the alarm 2 registers. If the A2IE bit is logic 1 and the INTCN bit is set to logic 1, the SQW/INT pin is also asserted. A2F is cleared when written to logic 0. This bit can only be written to logic 0. Attempting to write to logic 1 leaves the value unchanged. Bit 0/Alarm 1 Flag (A1F). A logic 1 in the alarm 1 flag bit indicates that the time matched the alarm 1 registers. If the A1IE bit is logic 1 and the INTCN bit is set to logic 1, the SQW/INT pin is also asserted. A1F is cleared when written to logic 0. This bit can only be written to logic 0. Attempting to write to logic 1 leaves the value unchanged. 2-Wire Serial Data Bus The DS1375 supports a bidirectional 2-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. A master device that generates the serial clock (SCL), controls the bus access, and generates the START and STOP conditions must control the bus. The DS1375 operates as a slave on the 2-wire bus. Connections to the bus are made through the open-drain I/O lines SDA and SCL. Within the bus specifications a standard mode (100kHz max clock rate) and a fast mode (400kHz max clock rate) are defined. The DS1375 works in both modes. SDA MSB SLAVE ADDRESS R/W DIRECTION BIT ACKNOWLEDGEMENT SIGNAL FROM RECEIVER ACKNOWLEDGEMENT SIGNAL FROM RECEIVER SCL 1 2 START CONDITION 6 7 8 9 1 2 3–7 8 ACK 9 ACK REPEATED IF MORE BYTES ARE TRANSFERRED STOP CONDITION OR REPEATED START CONDITION Figure 3. 2-Wire Data Transfer Overview _____________________________________________________________________ 9 DS1375 Bit 7 <RW> <WORD <SLAVE ADDRESS (n)> <DATA (n)> <DATA (n + 1)> <DATA (n + X)> ADDRESS> S 1101000 0 A XXXXXXXX A XXXXXXXX A XXXXXXXX A XXXXXXXX A P S — START DATA TRANSFERRED A — ACKNOWLEDGE (X + 1 BYTES + ACKNOWLEDGE) P — STOP R/W — READ/WRITE OR DIRECTION BIT ADDRESS = D0H Figure 4. Slave Receiver Mode (Write Mode) tion is transferred byte-wise and each receiver acknowledges with a ninth bit. 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 that 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. Figures 4 and 5 detail how data transfer is accomplished on the 2-wire 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 master transmits the first byte (the slave address). 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 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. 10 <SLAVE <DATA (n)> <DATA (n + 1)> <DATA (n + 2)> <DATA (n + X)> ADDRESS> S 1101000 1 A XXXXXXXX A XXXXXXXX A XXXXXXXX A XXXXXXXX A P <RW> DS1375 2-Wire Digital Input RTC with Alarm DATA TRANSFERRED S — START (X + 1 BYTES + ACKNOWLEDGE) A — ACKNOWLEDGE NOTE: LAST DATA BYTE IS FOLLOWED BY P — STOP A NOT ACKNOWLEDGE (A) SIGNAL A — NOT ACKNOWLEDGE R/W — READ/WRITE OR DIRECTION BIT ADDRESS = D0H Figure 5. Slave Transmitter Mode (Read Mode) The DS1375 can operate in the following two modes: Slave Receiver Mode (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 master generates the START condition. The slave address byte contains the 7-bit DS1375 address, which is 1101000, followed by the direction bit (R/W), which is 0 for a write. After receiving and decoding the slave address byte, the DS1375 outputs an acknowledge on SDA. After the DS1375 acknowledges the slave address + write bit, the master transmits a word address to the DS1375. This sets the register pointer on the DS1375, with the DS1375 acknowledging the transfer. The master can then transmit zero or more bytes of data, with the DS1375 acknowledging each byte received. The register pointer increments after each data byte is transferred. The master generates a STOP condition to terminate the data write. Slave Transmitter Mode (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. The DS1375 transmits serial data on SDA 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 master generates the START condition. The slave address byte contains the 7-bit DS1375 address, which is 1101000, followed by the direction bit (R/W), which is 1 for a read. After receiving and decoding the slave address byte, the DS1375 outputs an acknowledge on SDA. The DS1375 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 ____________________________________________________________________ 2-Wire Digital Input RTC with Alarm Package Information For the latest package outline information, go to www.maxim-ic.com/package_drawings/21-0137D.pdf. Chip Information TRANSISTOR COUNT: 11,797 PROCESS: CMOS SUBSTRATE CONNECTED TO GROUND Thermal Information Theta-JA: 41°C/W Theta-JC: 2°C/W Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim 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 ____________________ 11 © 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. DS1375 the initiation of a read mode, the first address that is read is the last one stored in the register pointer. The DS1375 must receive a not acknowledge to end a read.