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MQ162-01
Application Manual
Real Time Clock Module
RTC-72421/ 72423

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   Also See for Epson RTC-72421

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   Summary of Contents for Epson RTC-72421

  • Page 1

    MQ162-01 Application Manual Real Time Clock Module RTC-72421/ 72423...

  • Page 2

    • Seiko Epson reserves the right to make changes to this material without notice. • Seiko Epson does not assume any liability of any kind arising out of any inaccuracies contained in this material or due to its application or use in any product or circuit and, further, there is no representation that this material is applicable to products requiring high level reliability, such as, medical products.

  • Page 3: Table Of Contents

    CONTENTS Overview ---------------------------------------------------------------------------------------------------1 Block diagram --------------------------------------------------------------------------------------------2 Pin connections ------------------------------------------------------------------------------------------2 Pin functions ----------------------------------------------------------------------------------------------3 Characteristics--------------------------------------------------------------------------------------------4 1. Absolute maximum ratings ------------------------------------------------------------------------------------------------4 2. Operating conditions --------------------------------------------------------------------------------------------------------4 3. Frequency characteristics and current consumption characteristics -------------------------------------------4 4. Electrical characteristics (DC characteristics) ------------------------------------------------------------------------5 Switching characteristics (AC characteristics) ---------------------------------------------------6 1.

  • Page 4

    CONTENTS Using the RTC-72421/RTC-72423 ----------------------------------------------------------------16 1. Power-on procedure (initialization) ------------------------------------------------------------------------------------16 2. Read/write of S to W registers -----------------------------------------------------------------------------------------18 3. Write to 30-second ADJ bit ----------------------------------------------------------------------------------------------18 4. Using the CS pin ----------------------------------------------------------------------------------------------------------19 (1) Functions -----------------------------------------------------------------------------------------------------------------19 (2) Timing ---------------------------------------------------------------------------------------------------------------------19 (3) Note-----------------------------------------------------------------------------------------------------------------------19 Power supply circuit example -----------------------------------------------------------------------19 Examples of connection to general-purpose microprocessor ------------------------------20 1.

  • Page 5: Overview

    Pins and functions compatible with the SMC5242 series Overview The RTC-72421/RTC-72423 module is a real time clock that can be connected directly to a microprocessor's bus. Its built-in crystal unit enables highly accurate timekeeping with no physical access required for adjustment and, since there is no need to connect external components, mounting and other costs can be reduced.

  • Page 6: Block Diagram

    RTC-72421/72423 Block diagram Pin connections RTC-72421 RTC-72423 The (V ) pins are at the same electrical level as V . Do not connect these pins externally. The N.C. pins are not connected internally. Ground them in order to prevent noise.

  • Page 7: Pin Functions

    Pin functions Signal Pin No. Input/ Function RTC-72421 RTC-72423 Output Connect these pins to a bidirectional data bus or CPU data bus. Use this bus to read to and write from the internal counter and registers. CS-1 Mode of D...

  • Page 8: Characteristics

    RTC-72421/72423 Characteristics 1. Absolute maximum ratings ° 5 ° 5 ° 5 ° ° 0 ° ° 0 ° 0 2. Operating conditions ° µs 3. Frequency characteristics and current consumption characteristics ± ± ° 5 ∆ 0 f ±...

  • Page 9: Electrical Characteristics (dc Characteristics)

    4. Electrical characteristics (DC characteristics) µA µA µA Page-5...

  • Page 10: Switching Characteristics (ac Characteristics)

    RTC-72421/72423 Switching characteristics (AC characteristics) 1. When ALE is used Write mode =5V±0.5V,RTC-72421:Ta=-10°C to +70°C, RTC-72423:Ta=-40°C to +85°C) Read mode =5V±0.5V,RTC-72421:Ta=-10°C to +70°C, RTC-72423:Ta=-40°C to +85°C) Page-6...

  • Page 11

    (1) Write mode (2) Read mode Page-7...

  • Page 12: When Ale Is Fixed At

    RTC-72421/72423 2. When ALE is fixed at V Write mode =5V±0.5V, RTC-72421:Ta=-10°C to +70°C, RTC-72423:Ta=-40°C to +85°C) Read mode =5V±0.5V, RTC-72421:Ta=-10°C to +70°C, RTC-72423:Ta=-40°C to +85°C) (1) Write mode (2) Read mode (3) Read/write recovery mode Page-8...

  • Page 13: Registers

    72423" on page 16. (4) The TEST bit of control register F is used by EPSON for testing. Operation cannot be guaranteed if 1 is written to this bit, so make sure that it is set to 0 during power-on initialization.

  • Page 14: Functions Of Register Bits (overview)

    RTC-72421/72423 3. Functions of register bits (overview) t i r t i r s t i s t i o l l d i l t i r x i f t i r . t i , t i...

  • Page 15: Register Description

    The main leap and ordinary years since 1900 and into the future are listed on the right. [Leap years in the RTC-72421/72423] To identify leap years, the RTC-72421/RTC-72423 checks whether or not the year digits are divisible by four. As implied above, 2000 will be a leap year, and so no further correction will be necessary in that case.

  • Page 16: C D Register (control Register

    RTC-72421/72423 2. C register (control register D) (1) HOLD bit (D Use the HOLD bit when accessing the S and W registers. For details, see "Read/write of S to W registers" on page When the HOLD bit is 1, any incrementation in the count is held within the RTC. The held incrementation is automatically compensated for when the HOLD bit becomes 0.

  • Page 17: 30-second Adj Bit

    The output levels of the STD.P pin are low (down) and open circuit (up). Note: If the STD.P pin output remains low as set, subsequently generated interrupts are ignored. In order to prevent interrupts from being overlooked, write 0 to the IRQ FLAG bit before the next interrupt is generated, to return the STD.P pin to high.

  • Page 18: Itrpt/stnd Bit

    RTC-72421/72423 1. Fixed-period pulse output mode (ITRPT/STND=0) The output levels of the STD.P pin are low (down) and open circuit (up). 2. Fixed-period interrupt mode (ITRPT/STND=1) The output levels of the STD.P pin are low (down) and open circuit (up).

  • Page 19: C F Register (control Register

    24/12 bit. (4) TEST bit (D The TEST bit is used by EPSON for test purposes. Operation cannot be guaranteed if 1 is written to this bit, so make sure that it is set to 0 during power-on initialization.

  • Page 20: Using The Rtc-72421/rtc-72423

    RTC-72421/72423 Using the RTC-72421/RTC-72423 1. Power-on procedure (initialization) When power is turned on, the contents of all registers and the output from the STD.P pin are undefined. Therefore, all the registers must be initialized after power on. Follow the procedure given below for initialization.

  • Page 21

    (C) Stopping and resetting the counter (A)Starting the count Wait 250 µs (B)Checking the status of the BUSY bit (C)Stopping and resetting the counter Page-17...

  • Page 22: Read/write Of S To W Registers

    RTC-72421/72423 Read/write of S to W registers Use one of the procedures shown below to access registers other than the control registers (C , and C ) while the RTC is operating. Note that the control registers can be accessed regardless of the status of the BUSY bit.

  • Page 23: Using The Cs Pin

    4. Using the CS The RTC-72421/RTC-72423 has 2 chip-select signal systems: and CS . Use as chip-select for ordinary bus access. CS is not only used for CPU bus control, it also has the main function of switching between standby mode and operating mode.

  • Page 24: Examples Of Connection To General-purpose Microprocessor

    RTC-72421/72423 Examples of connection to general-purpose microprocessor When connecting the RTC-72421/RTC-72423 to a microprocessor, carefully check the AC timings of both the RTC and the microprocessor. 1. Connection to multiplexed bus type The resistors on the lines are not necessary if the CPU does not have a HALT or HOLD state.

  • Page 25: Reference Data

    Reference data 1. Connection to multiplexed bus type (typical) Finding the frequency stability (clock error) 1. The frequency-temperature characteristics can be approximated by the following equation: ∆f (ppm)=α(θ -θ 2. To determine the overall clock accuracy, add the frequency tolerance and the voltage characteristics: ∆f/f(ppm)=∆f/f + ∆f + ∆f...

  • Page 26: External Dimensions

    RTC-72421/72423 External dimensions 1. RTC-72421 2. RTC-72423 Unless otherwise stated, all units are mm. Marking layout Note: The illustration is a general representation of the content and location of information on the label, and is not a detailed specification of the typeface, size, or positioning of printing used on the label.

  • Page 27: Application Notes

    Application notes 1. Notes on handling In order to enable the RTC-72421/RTC-72423 module to operate at low power levels, C-MOS circuitry was used in the design of the chip. To prevent damage to this RTC, note the following points: (1) Static electricity While this module has built-in circuitry designed to protect it against electrostatic discharge, the chip could still be damaged by a large discharge of static electricity.

  • Page 28: Notes On Mounting

    2. Notes on mounting (1) Soldering temperature conditions i. RTC-72421 Solder is used on the built-in crystal unit. Therefore, if the temperature within the package exceeds 150°C, the characteristics of the crystal unit will be degraded and it may be damaged. Either use a soldering bath or solder by hand.

  • Page 29

    EPSON HONG KONG LTD. 20/F., Harbour Centre, 25 Harbour Road, Wanchai, HONG KONG Phone: (852) 2585-4600 Fax: (852) 2827-2152 EPSON TAIWAN TECHNOLOGY & TRADING LTD. 10F, No.287, Nanking East Road, Sec.3, Taipei, TAIWAN, R.O.C. Phone: (886) 2-717-7360 Fax: (886)2-718-9366 EPSON SINGAPORE PTE. LTD.

This manual also for:

Rtc-72423

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