M41T256Y 256 Kbit (32K x8) SERIAL RTC FEATURES SUMMARY ■ 5V OPERATING VOLTAGE ■ SERIAL INTERFACE SUPPORTS EXTENDED I2C BUS ADDRESSING (400 KHz) ■ AUTOMATIC SWITCH-OVER and DESELECT CIRCUITRY ■ POWER-FAIL DESELECT VOLTAGES: ■ – M41T256Y: VCC = 4.5 to 5.5V; VPFD = 4.2 < VPFD < 4.5V COUNTERS FOR TENTHS/HUNDREDTHS OF SECONDS, SECONDS, MINUTES, HOURS, DAY, DATE, MONTH, and YEAR ■ PROGRAMMABLE SOFTWARE CLOCK CALIBRATION ■ 32,752 BYTES OF GENERAL PURPOSE RAM ■ MICROPROCESSOR POWER-ON RESET ■ HOLDS MICROPROCESSOR IN RESET UNTIL SUPPLY VOLTAGE REACHES STABLE OPERATING LEVEL ■ AUTOMATIC ADDRESS-INCREMENTING ■ TAMPER INDICATION CIRCUIT with TIMESTAMP ■ SLEEP MODE FUNCTION ■ PACKAGING INCLUDES A 44-LEAD SOIC and SNAPHAT® TOP (to be ordered separately) ■ SOIC PACKAGE PROVIDES DIRECT CONNECTION FOR A SNAPHAT® TOP WHICH CONTAINS THE BATTERY and CRYSTAL March 2003 Rev. 2.2 Figure 1. 44-pin, Hatless SOIC Package 44 1 SO44 (MT) Figure 2. 44-pin SOIC Package SNAPHAT (SH) Crystal/Battery 44 1 SOH44 (MH) 1/26 M41T256Y TABLE OF CONTENTS SUMMARY DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Logic Diagram (Figure 3.) . . . . . . . . . . . . . . Signal Names (Table 1.) . . . . . . . . . . . . . . . 44-pin SOIC Connections (MT) (Figure 4.) . Block Diagram (Figure 6.) . . . . . . . . . . . . . . ...... ...... ...... ...... ....... ....... ....... ....... ...... ...... ...... ...... ....... ....... ....... ....... ...... ...... ...... ...... ...........4 ...........4 ...........5 ...........5 MAXIMUM RATING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Absolute Maximum Ratings (Table 2.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 DC AND AC PARAMETERS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 DC and AC Measurement Conditions (Table 3.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 AC Testing Input/Output Waveforms (Figure 7.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Capacitance (Table 4.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 DC Characteristics (Table 5.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Crystal Electrical Characteristics (Externally Supplied) (Table 6.). . . . . . . . . . . . . . . . . . . . . . . . . . . 8 OPERATING MODES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2-Wire Bus Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Serial Bus Data Transfer Sequence (Figure 8.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Acknowledgement Sequence (Figure 9.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Bus Timing Requirements Sequence (Figure 10.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 AC Characteristics (Table 7.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 READ Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 WRITE Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Slave Address Location (Figure 11.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 READ Mode Sequence (Figure 12.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Alternate READ Mode Sequence (Figure 13.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 WRITE Mode Sequence (Figure 14.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Data Retention Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Sleep Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Power Down/Up Mode AC Waveforms (Figure 15.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Power Down/Up AC Characteristics (Table 8.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 CLOCK OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Reading the Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Setting the Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Stopping and Starting the Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 TIMEKEEPER® Register Map (Table 9.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Power-on Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2/26 M41T256Y Tamper Indication Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Tamper Event Time-Stamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Battery Low Warning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Preferred Power-on/Battery Attach Defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Preferred Default Values (Table 10.). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Crystal Accuracy Across Temperature (Figure 16.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Clock Calibration (Figure 17.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 PACKAGE MECHANICAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 PART NUMBERING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 SNAPHAT® Battery Table (Table 15.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4 REVISION HISTORY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3/26 M41T256Y SUMMARY DESCRIPTION The M41T256Y Serial TIMEKEEPER ® SRAM is a low power 256 Kbit static CMOS SRAM organized as 32K words by 8 bits. A built-in 32.768 kHz oscillator (external crystal controlled) and 8 bytes of the SRAM (see Figure 9, page 17) are used for the clock/calendar function and are configured in binary coded decimal (BCD) format. Addresses and data are transferred serially via a two line, bi-directional I2C interface. The built-in address register is incremented automatically after each WRITE or READ data byte. The M41T256Y has a built-in power sense circuit which detects power failures and automatically switches to the battery supply when a power failure occurs. The energy needed to sustain the SRAM and clock operations can be supplied by a lithium button-cell supply when a power failure occurs. Functions available to the user include a non-volatile, time-of-day clock/calendar, and Power-on Reset. The eight clock address locations contain the year, month, date, day, hour, minute, second, and tenths/hundredths of seconds in 24hour BCD format. Corrections for 28, 29 (leap year - valid until year 2100), 30 and 31 day months are made automatically. The first clock address loca- Table 1. Signal Names Figure 3. Logic Diagram XI(1) Oscillator Input XO(1) Oscillator Output FT Frequency Test (Open drain) RST Reset Output (Open drain) RST SCL Serial Clock Input FT SDA Serial Data Input/Output VCC Supply Voltage VBAT(1) Battery Supply Voltage VSS Ground TP Tamper Input (1) VCC VBAT XI(1) XO(1) SCL tion (7FF8h) stores the clock software calibration settings as well as the Write Clock Bit. The M41T256Y is supplied in a 44-lead SOIC SNAPHAT® package (MH - which integrates both crystal and battery in a single SNAPHAT top) or a 44-pin “hatless” SOIC (MT). The 44-pin, 330mil SOIC provides sockets with gold-plated contacts at both ends for direct connection to a separate SNAPHAT housing containing the battery and crystal. The unique design allows the SNAPHAT battery/crystal package to be mounted on top of the SOIC package after the completion of the surface-mount process. Insertion of the SNAPHAT housing after reflow prevents potential battery and crystal damage due to the high temperatures required for device surface-mounting. The SNAPHAT housing is also keyed to prevent reverse insertion. The 44-pin SOIC and crystal/battery packages are shipped separately in plastic, anti-static tubes or in Tape & Reel form. For the 44-lead SOIC, the battery/crystal package (e.g., SNAPHAT) part number is “M4Txx-BR12SH” (see Table 15, page 24). Caution: Do not place the SNAPHAT battery/crystal top in conductive foam, as this will drain the lithium, button-cell battery. M41T256Y SDA TP VSS AI04754b Note: 1. For 44-pin SNAPHAT (MT) package only. 4/26 Note: 1. For 44-pin SNAPHAT (MT) package only. M41T256Y Figure 4. 44-pin SOIC Connections (MT) XO XI NF RST NF NF NF NF NF NF NF TP NC NF NF NF NF SDA VSS VSS NC VSS Figure 5. 44-pin SOIC (MH - SNAPHAT) VCC NC NC NC FT NF NF NF NF NF NF NC NC NF SCL NC NF NF NF NF NF BAT+ 1 44 43 2 3 42 4 41 5 40 6 39 7 38 8 37 36 9 10 35 11 M41T256Y 34 12 33 13 32 14 31 15 30 29 16 28 17 27 18 19 26 20 25 21 24 22 23 NC NC NF RST NF NF NF NF NF NF NF TP NC NF NF NF NF SDA VSS VSS NC VSS 1 44 43 2 3 42 4 41 5 40 6 39 7 38 8 37 36 9 10 35 11 M41T256Y 34 12 33 13 32 14 31 15 30 29 16 28 17 27 18 19 26 20 25 21 24 22 23 AI04755b VCC NC NC NC FT NF NF NF NF NF NF NC NC NF SCL NC NF NF NF NF NF NC AI07022 Note: No Function (NF) must be tied to VSS. Figure 6. Block Diagram PULL-UP TO CHIP VCC REAL TIME CLOCK CALENDAR 32,752 BYTES USER RAM SDA I2C INTERFACE RTC & CALIBRATION SCL TAMPER BIT 32KHz OSCILLATOR Crystal FT(1) TP POWER VCC VBAT VBL= 2.5V COMPARE VSO = VBAT COMPARE BL VPFD = 4.38V COMPARE POR RST(1) AI04759 Note: 1. Open drain output 5/26 M41T256Y MAXIMUM RATING Stressing the device above the rating listed in the “Absolute Maximum Ratings” table may cause permanent damage to the device. These are stress ratings only and operation of the device at these or any other conditions above those indicated in the Operating sections of this specification is not implied. Exposure to Absolute Maximum Rating conditions for extended periods may affect device reliability. Refer also to the STMicroelectronics SURE Program and other relevant quality documents. Table 2. Absolute Maximum Ratings Symbol TSTG TSLD(1) Parameter Storage Temperature (VCC Off, Oscillator Off) Lead Solder Temperature for 10 seconds Value Unit SNAPHAT® –40 to 85 °C SOIC –55 to 125 °C 260 °C –0.3 to VCC + 0.3 V VIO Input or Output Voltages VCC Supply Voltage –0.3 to 7.0 V IO Output Current 20 mA PD Power Dissipation 1 W Note: 1. Reflow at peak temperature of 215°C to 225°C for < 60 seconds (total thermal budget not to exceed 180°C for between 90 to 120 seconds). CAUTION: Negative undershoots below –0.3V are not allowed on any pin while in the Battery Back-up mode. CAUTION: Do NOT wave solder SOIC to avoid damaging SNAPHAT sockets. 6/26 M41T256Y DC AND AC PARAMETERS This section summarizes the operating and measurement conditions, as well as the DC and AC characteristics of the device. The parameters in the following DC and AC Characteristic tables are derived from tests performed under the Measure- ment Conditions listed in the relevant tables. Designers should check that the operating conditions in their projects match the measurement conditions when using the quoted parameters. Table 3. DC and AC Measurement Conditions Parameter M41T256Y VCC Supply Voltage 4.5 to 5.5V Ambient Operating Temperature –25 to 70°C Load Capacitance (CL) 100pF Input Rise and Fall Times ≤ 50ns Input Pulse Voltages 0.2VCC to 0.8VCC Input and Output Timing Ref. Voltages 0.3VCC to 0.7VCC Figure 7. AC Testing Input/Output Waveforms 0.8VCC 0.7VCC 0.3VCC 0.2VCC AI02568 Table 4. Capacitance Parameter(1,2) Symbol CIN CIO(3) tLP Max Unit 7 pF 1000 pF Input / Output Capacitance 10 pF Low-pass filter input time constant (SDA and SCL) 50 ns Input Capacitance Input Capacitance (Tamper Pin) Min Note: 1. Effective capacitance measured with power supply at 5V; sampled only, not 100% tested. 2. At 25°C, f = 1MHz. 3. Outputs deselected. 7/26 M41T256Y Table 5. DC Characteristics Sym Test Condition(1) Parameter Min Typ Max Unit 1.5 1.9 µA 1.0 1.4 µA f = 400kHz 1.4 3.0 mA SCL, SDA = VCC – 0.3V 1.0 2.5 mA 0V ≤ VIN ≤ VCC ±1 µA 0V ≤ VOUT ≤ VCC ±1 µA TA = 25°C, VCC = 0V, VBAT = 3.0V Battery Current OSC ON IBAT Battery Current OSC OFF ICC1 Supply Current ICC2 Supply Current (Standby) Input Leakage Current ILI ILO(2) Output Leakage Current VIH Input High Voltage 0.7VCC VCC + 0.3 V VIHB Input High Voltage in Battery Backup for Tamper Pin VBAT – Vdiode VBAT V Input Low Voltage –0.3 0.3VCC V VBAT Battery Voltage 2.5 3.5 V VOH Output High Voltage VCC + 0.3 V VIL VOL Output Low Voltage IOL = 3.0mA 0.4 V Output Low Voltage (Open Drain)(3) IOL = 10mA 0.4 V 4.50 V VPFD Power Fail Deselect VSO Battery Back-up Switchover RSW Switch Resistance on Tamper Pin 4.20 VBAT V Ω 500 Note: 1. Valid for Ambient Operating Temperature: TA = –25 to 70°C; VCC = 4.5 to 5.5V (except where noted). 2. Outputs deselected. 3. For RST and FT pin (Open Drain). Table 6. Crystal Electrical Characteristics (Externally Supplied) Symbol Parameter(1,2) f0 Resonant Frequency RS Series Resistance CL Load Capacitance Typ Min Max 32.768 kHz 35 12.5 Unit kΩ pF Note: 1. STMicroelectronics recommends the KDS DT-38: 1TA/1TC252E127, Tuning Fork Type (thru-hole) or the DMX-26S: 1TJS125FH2A212, (SMD) quartz crystal for industrial temperature operations. KDS can be contacted at [email protected] or http://www.kdsj.co.jp for further information on this crystal type. 2. Load capacitors are integrated within the M41T256Y. Circuit board layout considerations for the 32.768 kHz crystal of minimum trace lengths and isolation from RF generating signals should be taken into account. 8/26 M41T256Y OPERATING MODES The M41T256Y clock operates as a slave device on the serial bus. Access is obtained by implementing a start condition followed by the correct slave address (D0h). The 256K bytes contained in the device can then be accessed sequentially in the following order: 0-7FEF = General Purpose RAM 7FF0-7FF6 = Reserved 7FF7h = Tenths/Hundredths Register 7FF8h = Control Register 7FF9h = Seconds Register 7FFAh = Minutes Register 7FFBh = Hour Register 7FFCh = Tamper/Day Register 7FFDh = Date Register 7FFEh = Month Register 7FFFh = Year Register The M41T256Y clock continually monitors VCC for an out-of tolerance condition. Should VCC fall below VPFD, the device terminates an access in progress and resets the device address counter. Inputs to the device will not be recognized at this time to prevent erroneous data from being written to the device from an out-of-tolerance system. When VCC falls below VSO, the device automatically switches over to the battery and powers down into an ultra low current mode of operation to conserve battery life. As system power returns and VCC rises above VSO , the battery is disconnected, and the power supply is switched to external VCC. Write protection continues until VCC reaches VPFD plus tREC. For more information on Battery Storage Life refer to Application Note AN1012. 2-Wire Bus Characteristics The bus is intended for communication between different ICs. It consists of two lines: a bi-directional data signal (SDA) and a clock signal (SCL). Both the SDA and SCL lines must be connected to a positive supply voltage via a pull-up resistor. The following 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 the START condition. Stop data transfer. A change in the state of the data line, from Low to High, while the clock 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 may 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 stop conditions is not limited. The information is transmitted byte-wide and each receiver acknowledges with a ninth bit. By definition a device that gives out a message is called “transmitter,” the receiving device that gets the message is called “receiver.” The device that controls the message is called “master.” The devices that are controlled by the master are called “slaves.” Acknowledge. Each byte of eight bits is followed by one acknowledge clock pulse. This acknowledge clock pulse is a low level put on the bus by the receiver whereas the master generates an extra acknowledge related clock pulse. A slave receiver which is addressed is obliged to generate an acknowledge after the reception of each byte that has been clocked out of the slave transmitter. The device that acknowledges has to pull down the SDA line during the acknowledge clock pulse in such a way that the SDA line is a 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 receiver must signal an end of data to the slave transmitter by not generating an acknowledge on the last byte that has been clocked out of the slave. In this case the transmitter must leave the data line High to enable the master to generate the STOP condition. 9/26 M41T256Y Figure 8. Serial Bus Data Transfer Sequence DATA LINE STABLE DATA VALID (SCL) CLOCK (SDA) DATA START CONDITION CHANGE OF DATA ALLOWED STOP CONDITION AI04756 Figure 9. Acknowledgement Sequence CLOCK PULSE FOR ACKNOWLEDGEMENT START SCL FROM MASTER DATA OUTPUT BY TRANSMITTER 1 MSB 2 8 9 LSB DATA OUTPUT BY RECEIVER AI00601 10/26 M41T256Y Figure 10. Bus Timing Requirements Sequence SDA tBUF tHD:STA tHD:STA tF tR SCL tHIGH P S tLOW tSU:DAT tHD:DAT tSU:STA SR tSU:STO P AI00589 Table 7. AC Characteristics Parameter(1) Symbol fSCL SCL Clock Frequency tBUF Time the bus must be free before a new transmission can start tF Min Max Unit 0 400 kHz 1.3 SDA and SCL Fall Time tHD:DAT Data Hold Time tHD:STA µs 300 ns 0 µs START Condition Hold Time (after this period the first clock pulse is generated) 600 ns tHIGH Clock High Period 600 ns tLOW Clock Low Period 1.3 µs tR tSU:DAT(2) SDA and SCL Rise Time 300 ns Data Setup Time 100 ns tSU:STA START Condition Setup Time (only relevant for a repeated start condition) 600 ns tSU:STO STOP Condition Setup Time 600 ns Note: 1. Valid for Ambient Operating Temperature: TA = –25 to 70°C; VCC = 4.5 to 5.5V (except where noted). 2. Transmitter must internally provide a hold time to bridge the undefined region (300ns max) of the falling edge of SCL. 11/26 M41T256Y READ Mode In this mode the master reads the M41T256Y slave after setting the slave address (see Figure 11, page 12). Following the WRITE Mode Control Bit (R/W=0) and the Acknowledge Bit, the byte addresses A(0) and A(1) are written to the on-chip address pointer (MSB of address byte A(0) is a “Don’t care”). Next the START condition and slave address are repeated followed by the READ Mode Control Bit (R/W=1). At this point the master transmitter becomes the master receiver. The data byte which was addressed will be transmitted and the master receiver will send an acknowledge bit to the slave transmitter. The address pointer is only incremented on reception of an Acknowledge Clock. The M41T256Y slave transmitter will now place the data byte at address An+1 on the bus, the master receiver reads and acknowledges the new byte and the address pointer is incremented to An+2. This cycle of reading consecutive addresses will continue until the master receiver sends a STOP condition to the slave transmitter (see Figure 12, page 13). Note: Address pointer will wrap around from maximum address to minimum address if consecutive READ or WRITE cycles are performed. An alternate READ Mode may also be implemented whereby the master reads the M41T256Y slave without first writing to the (volatile) address pointer. The first address that is read is the last one stored in the pointer (see Figure 13, page 13). WRITE Mode In this mode the master transmitter transmits to the M41T256Y slave receiver. Bus protocol is shown in Figure Figure 14, page 13. Following the START condition and slave address, a logic '0' (R/ W=0) is placed on the bus and indicates to the addressed device that byte addresses A(0) and A(1) will follow and is to be written to the on-chip address pointer (MSB of address byte A(0) is a “Don’t care”). The data byte to be written to the memory is strobed in next and the internal address pointer is incremented to the next memory location within the RAM on the reception of an acknowledge bit. The M41T256Y slave receiver will send an acknowledge bit to the master transmitter after it has received the slave address (see Figure 11, page 12) and again after it has received each address byte. Figure 11. Slave Address Location R/W START A 1 LSB MSB SLAVE ADDRESS 1 0 1 0 0 0 AI00602 Note: The most significant bit is sent first. 12/26 M41T256Y S ACK ACK DATA n ACK BUS ACTIVITY: BYTE ADDRESS (1) R/W START R/W BYTE ADDRESS (0) S ACK SDA LINE ACK BUS ACTIVITY: MASTER START Figure 12. READ Mode Sequence SLAVE ADDRESS STOP SLAVE ADDRESS P NO ACK DATA n+X AI04760 BUS ACTIVITY: STOP DATA n+X SLAVE ADDRESS P NO ACK DATA n+1 ACK DATA n ACK S ACK SDA LINE ACK BUS ACTIVITY: MASTER R/W START Figure 13. Alternate READ Mode Sequence AI00895 SLAVE ADDRESS STOP DATA n+X ACK ACK ACK BUS ACTIVITY: DATA n P ACK BYTE ADDRESS (1) BYTE ADDRESS (0) S ACK SDA LINE R/W BUS ACTIVITY: MASTER START Figure 14. WRITE Mode Sequence AI04761 13/26 M41T256Y Data Retention Mode With valid VCC applied, the M41T256Y can be accessed as described above with READ or WRITE Cycles. Should the supply voltage decay, the M41T256Y will automatically deselect, write protecting itself when VCC falls between VPFD (max) and VPFD (min). This is accomplished by internally inhibiting access to the clock registers. At this time, the Reset pin (RST) is driven active and will remain active until VCC returns to nominal levels. When VCC falls below the Battery Back-up Switchover Voltage (VSO), power input is switched from the VCC pin to the external battery and the clock registers and SRAM are maintained from the attached battery supply. All outputs become high impedance. On power up, when VCC returns to a nominal value, write protection continues for tREC. The RST signal also remains active during this time (see Figure 15, page 15). For a further more detailed review of lifetime calculations, please see Application Note AN1012. Sleep Mode In order to minimize the battery current draw while in storage, the M41T256Y provides the user with a battery “Sleep Mode,” which disconnects the RAM memory array from the external Lithium battery normally used to provide non-volatile operation in the absence of VCC. This can significantly extend the lifetime of the battery, when non-volatile operation is not needed. 14/26 Note: The Sleep Mode will remove power from the RAM array only and not affect the data retention of the TIMEKEEPER Registers (7FF0h through 7FFFh - this includes the Calibration Register). The Sleep Mode (SLP) Bit located in register 7FF8h (D6), must be set to a '1' by the user while the device is powered by VCC. This will “arm” the Sleep Mode latch, but not actually disconnect the RAM array from power until the next power-down cycle. This protects the user from immediate data loss in the event he inadvertently sets the SLP Bit. Once VCC falls below VSO (VBAT), the Sleep Mode circuit will be engaged and the RAM array will be isolated from the battery, resulting in both a lower battery current, and a loss of RAM data. Note: Upon initial battery attach or initial power application without the battery, the state of the SLP Bit will be undetermined. Therefore, the SLP Bit should be initialized to '0' by the user. Additional current reduction can be achieved by setting the STOP (ST) Bit in register 7FF9h (D7), turning off the clock oscillator. This combination will result in the longest possible battery life, but also loss of time and data. When the device is again powered-up, the user should first read the SLP Bit to determine if the device is currently in Sleep Mode, then reset the bit to '0' in order to disable the Sleep Mode (this will NOT be automatically taken care of during the power-up). Note: See AN1570, “M41T256Y Sleep Mode Function” for more information on Sleep Mode and battery lifetimes. M41T256Y Figure 15. Power Down/Up Mode AC Waveforms VCC VPFD (max) VPFD (min) VSO tF tR tFB tRB tDR INPUTS RECOGNIZED tREC DON'T CARE RECOGNIZED RST HIGH-Z OUTPUTS VALID VALID (PER CONTROL INPUT) (PER CONTROL INPUT) AI04757 Table 8. Power Down/Up AC Characteristics Symbol Parameter(1) Min Typ Max Unit tF(2) VPFD (max) to VPFD (min) VCC Fall Time 300 µs tFB(3) VPFD (min) to VSS VCC Fall Time 10 µs tR VPFD (min) to VPFD (max) VCC Rise Time 10 µs tRB VSS to VPFD (min) VCC Rise Time 1 µs tREC Power up Deselect Time 40 tDR Expected Data Retention Time (OSC On, Sleep Mode Off) 15(4) 200 ms YEARS Note: 1. Valid for Ambient Operating Temperature: TA = –25 to 70°C; VCC = 4.5 to 5.5V (except where noted). 2. VPFD (max) to VPFD (min) fall time of less than tF may result in deselection/write protection not occurring until 200µs after VCC passes VPFD (min). 3. VPFD (min) to VSS fall time of less than tFB may cause corruption of RAM data. 4. At 25°C and VCC = 0V, using a BR2330 Li Battery. This drops to 7.2 years when using the M4T32-BR12SH with the oscillator running. 15/26 M41T256Y CLOCK OPERATION Year, Month, and Date are contained in the last three registers of the TIMEKEEPER ® Register Map (see Table 9). Bits D0 through D2 of the next register contain the Day (day of week). Finally, there are the registers containing the Seconds, Minutes, and Hours, respectively. The first clock register is the Control Register (this is described in the Clock Calibration section). The nine Clock Registers may be read one byte at a time, or in a sequential block. The Control Register (Address location 7FF8h) may be accessed independently. Provision has been made to assure that a clock update does not occur while any of the nine clock addresses are being read. If a clock address is being read, an update of the clock registers will be halted. This will prevent a transition of data during the read. Reading the Clock The nine byte clock register (see Table 9) is used to both set the clock and to read the date and time from the clock, in a binary coded decimal format. The system-to-user transfer of clock data will be halted whenever the address being read is a clock address (7FF9h to 7FFFh). The update will resume either due to a Stop Condition or when the pointer increments to a RAM address. This prevents reading data in transition. The TIMEKEEPER® cells in the Register Map are only data registers and not actual clock counters, so 16/26 updating the registers can be halted without disturbing the clock itself. Setting the Clock Bit D7 of the Control Register (7FF8h) is the Write Clock Bit. Setting the Write Clock Bit to a '1' will allow the user to write the desired Day, Date, and Time data in 24-hour BCD format. Resetting the Write Clock Bit to a '0' then transfers the values of all time registers (7FF8h-7FFFh) to the actual clock counters and resets the internal divider (or clock) chain. Note: The Tenths/Hundredths of Seconds Register will automatically be reset to zero when the WRITE Clock Bit is set. Other register bits such as FT, TEB, and ST may be written without setting the WC Bit. In such cases, the clock data will be undisturbed and will retain their previous values. Stopping and Starting the Oscillator The oscillator may be stopped at any time. If the device is going to spend a significant amount of time on the shelf, the oscillator can be turned off to minimize current drain on the battery. The Stop Bit (ST) is the most significant bit of the Seconds Register. Setting it to '1' stops the oscillator. Setting it to '0' restarts the oscillator in approximately one second. M41T256Y Table 9. TIMEKEEPER® Register Map Data Address D7 7FFFh D6 D5 D4 D3 D2 10 Years D0 Function/Range BCD Format Year Year 00-99 Month Month 01-12 Date: Day of Month Date 01-31 Tamper/Day 0-1/01-07 Hours (24 Hour Format) Hours 00-23 7FFEh 0 0 7FFDh 0 0 7FFCh BL FT 7FFBh 0 0 7FFAh 0 10 Minutes Minutes Minutes 00-59 7FF9h ST 10 Seconds Seconds Seconds 00-59 7FF8h WC 7FF7h SLP 0 D1 10M 10 Date TEB TB 0 10 Hours S Day of Week Calibration 0.1 Seconds Control 0.01 Seconds Seconds 7FF6h X X X X X X X X Reserved 7FF5h X X X X X X X X Reserved 7FF4h X X X X X X X X Reserved 7FF3h X X X X X X X X Reserved 7FF2h X X X X X X X X Reserved 7FF1h X X X X X X X X Reserved 7FF0h X X X X X X X X Reserved 00-99 Keys: S = Sign Bit BL = Battery Low Flag (Read only bit) FT = Frequency Test Bit TB = Tamper Bit (Read only bit) ST = Stop Bit TEB = Tamper Enable Bit WC = Write Clock Bit 0 = Must be set to '0' X = '1' or '0' SLP = Sleep Mode Bit Note: 7FF0h through 7FF6h are invalid addresses and when read will return arbitrary data. 17/26 M41T256Y Power-on Reset The M41T256Y continuously monitors VCC. When VCC falls to the power fail detect trip point, the RST pulls low (open drain) and remains low on powerup for tREC after VCC passes VPFD (max). The RST pin is an open drain output and an appropriate pull-up resistor should be chosen to control rise time. Tamper Indication Circuit The M41T256Y provides an independent input pin, the Tamper Pin (TP) which can be used to monitor a signal which can result in the setting of the Tamper Bit (TB) if the Tamper Enable Bit (TEB) is set to a '1.' The Tamper Pin is triggered by being connected to VCC/VBAT through an external switch. This switch is normally open in the application, allowing the pin to be “floating” (internally latched to VSS when TEB is set). When this switch is closed (connecting the pin to VCC/VBAT), the Tamper Bit will be immediately set. This allows the user to determine if the device has been physically moved or tampered with. The Tamper Bit is a “read only” bit and is reset only by taking the Tamper Pin to ground and resetting the Tamper Enable Bit to '0.' This function operates both under normal power, and in battery back-up. If the switch closes during a power-down condition, the bit will still be set correctly. Note: Upon initial battery attach or initial power application without the battery, the state of TEB (and TB) will be undetermined. Therefore TEB must be initialized to a '0.' Tamper Event Time-Stamp If a tamper occurs, not only will the Tamper Bit be set, but the event will also automatically be timestamped. This is accomplished by freezing the normal update of the clock registers (7FF7h through 7FFFh) immediately following a tamper event. Thus, when tampering occurs, the user may first read the time registers to determine exactly when the tamper event occurred, then re-enable the clock update to the current time (and reset the Tamper Bit, TB) by resetting the Tamper Enable Bit (TEB). The time update will then resume, and after either a Stop Condition or incrementing the address 18/26 pointer to a RAM address and back, the clock can be read to determine the current time. Note: The Tamper Bit (TB) must always be set to '0' in order to read the current time. Calibrating the Clock The M41T256Y is driven by a quartz controlled oscillator with a nominal frequency of 32,768 Hz. The devices are tested not exceed +/–35 PPM (parts per million) oscillator frequency error at 25oC, which equates to about +/–1.53 minutes per month. When the Calibration circuit is properly employed, accuracy improves to better than +1/–2 PPM at 25°C. The oscillation rate of crystals changes with temperature (see Figure 16, page 20). Therefore, the M41T256Y design employs periodic counter correction. The calibration circuit adds or subtracts counts from the oscillator divider circuit at the divide by 256 stage, as shown in Figure 17, page 20. The number of times pulses which are blanked (subtracted, negative calibration) or split (added, positive calibration) depends upon the value loaded into the five Calibration bits found in the Control Register. Adding counts speeds the clock up, subtracting counts slows the clock down. The Calibration bits occupy the five lower order bits (D4-D0) in the Control Register (7FF8h). These bits can be set to represent any value between 0 and 31 in binary form. Bit D5 is a Sign Bit; '1' indicates positive calibration, '0' indicates negative calibration. Calibration occurs within a 64 minute cycle. The first 62 minutes in the cycle may, once per minute, have one second either shortened by 128 or lengthened by 256 oscillator cycles. If a binary '1' is loaded into the register, only the first 2 minutes in the 64 minute cycle will be modified; if a binary 6 is loaded, the first 12 will be affected, and so on. Therefore, each calibration step has the effect of adding 512 or subtracting 256 oscillator cycles for every 125,829,120 actual oscillator cycles, that is +4.068 or –2.034 PPM of adjustment per calibration step in the calibration register. Assuming that the oscillator is running at exactly 32,768 Hz, each of the 31 increments in the Calibration byte would represent +10.7 or –5.35 seconds per month which corresponds to a total range of +5.5 or –2.75 minutes per month. M41T256Y Two methods are available for ascertaining how much calibration a given M41T256Y may require. The first involves setting the clock, letting it run for a month and comparing it to a known accurate reference and recording deviation over a fixed period of time. Calibration values, including the number of seconds lost or gained in a given period, can be found in Application Note AN934: TIMEKEEPER CALIBRATION. This allows the designer to give the end user the ability to calibrate the clock as the environment requires, even if the final product is packaged in a non-user serviceable enclosure. The designer could provide a simple utility that accesses the Calibration byte. The second approach is better suited to a manufacturing environment, and involves the use of the FT pin. The pin will toggle at 512Hz, when the Stop Bit (ST) is '0,' and the Frequency Test Bit (FT) is '1.' Any deviation from 512 Hz indicates the degree and direction of oscillator frequency shift at the test temperature. For example, a reading of 512.010124 Hz would indicate a +20 PPM oscillator frequency error, requiring a –10 (XX001010) to be loaded into the Calibration Byte for correction. Note that setting or changing the Calibration Byte does not affect the Frequency Test output frequency. The FT pin is an open drain output which requires a pull-up resistor to VCC for proper operation. A 500 to 10k resistor is recommended in order to control the rise time. The FT Bit is cleared on power-down. Battery Low Warning The M41T256Y automatically performs battery voltage monitoring upon power-up. The Battery Low (BL) Bit, Bit D7 of Day Register, will be asserted if the battery voltage is found to be less than approximately 2.5V. The BL Bit will remain asserted until completion of battery replacement and subsequent battery low monitoring tests, during the next power-up sequence. If a battery low is generated during a power-up sequence, this indicates that the battery is below approximately 2.5 volts and may not be able to maintain data integrity in the SRAM. Data should be considered suspect and verified as correct. A fresh battery should be installed. The battery may be replaced while VCC is applied to the device. The M41T256Y only monitors the battery when a nominal VCC is applied to the device. Thus applications which require extensive durations in the battery back-up mode should be powered-up periodically (at least once every few months) in order for this technique to be beneficial. Additionally, if a battery low is indicated, data integrity should be verified upon power-up via a checksum or other technique. Preferred Power-on/Battery Attach Defaults See Table 10, below. Table 10. Preferred Default Values Condition WC TEB(1) TB(1) FT ST(1) SLP(1) Battery Attach or Initial Power-up 0 X X 0 X X Power-Cycling (with battery) 0 UC UC 0 UC UC Note: 1. X = Undetermined; UC = Unchanged 19/26 M41T256Y Figure 16. Crystal Accuracy Across Temperature Frequency (ppm) 20 0 –20 –40 –60 –80 –100 ∆F = -0.038 ppm (T - T )2 ± 10% 0 F C2 –120 T0 = 25 °C –140 –160 –40 –30 –20 –10 0 10 20 30 40 50 60 70 80 Temperature °C AI00999 Figure 17. Clock Calibration NORMAL POSITIVE CALIBRATION NEGATIVE CALIBRATION AI00594B 20/26 M41T256Y PACKAGE MECHANICAL INFORMATION Figure 18. SOH44 – 44-lead Plastic, Hatless, Small Package Outline A2 A C B e CP D N E H A1 α L 1 SOH-C Note: Drawing is not to scale. Table 11. SOH44 – 44-lead Plastic, Hatless, Small Package Mechanical Data millimeters inches Symbol Typ Min A Max Typ Min Max 3.05 0 0.120 A1 0.05 0.36 0.002 0.014 A2 2.34 2.69 0.092 0.106 B 0.36 0.46 0.014 0.018 C 0.15 0.32 0.006 0.012 D 17.71 18.49 0.697 0.728 E 8.23 8.89 0.324 0.350 – – – – H 11.51 12.70 0.453 0.500 L 0.41 1.27 0.016 0.050 α 0° 8° 0° 8° N 44 e CP 0.81 0.032 44 0.10 0.004 21/26 M41T256Y Figure 19. SOH44 – 44-lead Plastic Small Outline, SNAPHAT, Package Outline A2 A C B eB e CP D N E H A1 α L 1 SOH-A Note: Drawing is not to scale. Table 12. SOH44 – 44-lead Plastic Small Outline, SNAPHAT, Package Mechanical Data mm inches Symb Typ Min A Typ Min 3.05 Max 0.120 A1 0.05 0.36 0.002 0.014 A2 2.34 2.69 0.092 0.106 B 0.36 0.46 0.014 0.018 C 0.15 0.32 0.006 0.012 D 17.71 18.49 0.697 0.728 E 8.23 8.89 0.324 0.350 – – – – eB 3.20 3.61 0.126 0.142 H 11.51 12.70 0.453 0.500 L 0.41 1.27 0.016 0.050 α 0° 8° 0° 8° N 44 e CP 22/26 Max 0.81 0.032 44 0.10 0.004 M41T256Y Figure 20. SH – 4-pin SNAPHAT Housing for 120mAh Battery & Crystal, Package Outline A1 A2 A eA A3 B L eB D E SHTK-A Note: Drawing is not to scale. Table 13. SH – 4-pin SNAPHAT Housing for 120mAh Battery & Crystal, Package Mechanical Data mm inches Symb Typ Min A Max Typ Min 10.54 Max 0.415 A1 8.00 8.51 0.315 .0335 A2 7.24 8.00 0.285 0.315 A3 0.38 0.015 B 0.46 0.56 0.018 0.022 D 21.21 21.84 0.835 0.860 E 17.27 18.03 0.680 .0710 eA 15.55 15.95 0.612 0.628 eB 3.20 3.61 0.126 0.142 L 2.03 2.29 0.080 0.090 23/26 M41T256Y PART NUMBERING Table 14. Ordering Information Scheme Example: M41T 256Y MT 7 TR Device Type M41T Supply Voltage and Write Protect Voltage 256Y = VCC = 4.5 to 5.5V; VPFD = 4.2 to 4.5V Package MT = 44-lead, Hatless SOIC MH(1) = SOH44 Temperature Range 7 = –25 to 70°C Shipping Method for SOIC blank = Tubes TR = Tape & Reel Note: 1. The SOIC package (SOH44) requires the battery package (SNAPHAT ®) which is ordered separately under the part number “M4Txx-BR12SH” in plastic tube or “M4Txx-BR12SHTR” in Tape & Reel form. Caution: Do not place the SNAPHAT battery package “M4Txx-BR12SH” in conductive foam as it will drain the lithium button-cell battery. For a list of available options (e.g., Speed, Package) or for further information on any aspect of this device, please contact the ST Sales Office nearest to you. Table 15. SNAPHAT® Battery Table Part Number M4T32-BR12SH 24/26 Description Lithium Battery (120mAh) SNAPHAT Package SH M41T256Y REVISION HISTORY Table 16. Document Revision History Date Rev. # Revision Details February 2002 1.0 First Issue 26-Apr-02 1.1 Addition of “Tamper Event Time-Stamp” text 31-May-02 1.2 Add Sleep Mode, 44-pin with SNAPHAT package (Figure 2, 5, 19, 20; Table 1, 2, 14, 15, 12, 13) 03-Jul-02 1.3 Modify Crystal Electrical Characteristics table footnotes (Table 6) 12-Jul-02 1.4 Added programmable Sleep Mode information to document (Figure 3, 4, 5, 6; Table 9, 10) 29-Jul-02 1.5 Add “Hatless” to package description (Figure 1, 18 and Table 14, 11) 20-Dec-02 2.0 ICC Characteristics changed (Table 5); Document promoted to “Datasheet” 04-Jan-03 2.1 Add VOL value (Table 5) 26-Mar-03 2.2 Update test condition (Table 8) 25/26 M41T256Y Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is registered trademark of STMicroelectronics All other names are the property of their respective owners. © 2003 STMicroelectronics - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan - Malaysia Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - U.S.A. www.st.com 26/26