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Epson RTC-72421 A Applications Manual

Real time clock module
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Application Manua
Real Time Clock Module
RTC-72421 A
RTC-72421 B
RTC-72423 A
Product Number



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  Summary of Contents for Epson RTC-72421 A

  • Page 1 MQ162-03 Application Manua Real Time Clock Module RTC-72421/72423 Model RTC-72421 A RTC-72421 B RTC-72423 A RTC-72423 Product Number Q4272421x000100 Q4272421x000200 Q4272423x000600 Q4272423x000700...
  • Page 2 • The information, applied circuit, program, using way etc., written in this material is just for reference. Seiko Epson does not assume any liability for the occurrence of infringing any patent or copyright of third party. This material does not authorize the licence for any patent or intellectual property rights.
  • Page 3: Table Of Contents

    RTC - 72421 / 72423 Overview ... 1 Block diagram ... 1 Terminal connections ... 2 Terminal functions... 3 Characteristics ... 4 1. Absolute maximum ratings... 4 2. Recommended operating conditions... 4 3. Frequency characteristics and current consumption characteristics... 4 4.
  • Page 4: Overview

    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 time-keeping 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 5: Terminal Connections

    RTC - 72421 / 72423 Terminal connections RTC-72421 STD.P The (V ) pins are at the same electrical level as V internally. Ground them in order to prevent noise. STD.P N.C. N.C. N.C. . Do not connect these pins externally. The N.C. pins are not connected Page - 2 RTC-72423 N.C.
  • Page 6: Terminal Functions

    RTC - 72421 / 72423 Terminal functions Pin No. Signal RTC-72421 RTC-72423 11 14 (Data bus) (Address bus) (Address Latch Enable) (WRite) (ReaD) 15,2 (Chip Select) STD.P (STanDard Pulse) 16, 17 N.C. Input/ou tput Connect these pines to a bi-directional data bus or CPU data bus. Use this bus to read to and write from the internal counter and registers.
  • Page 7: Characteristics

    RTC - 72421 / 72423 Characteristics 1. Absolute maximum ratings Item Symbol Supply voltage Input voltage Output voltage Storage temperature 2. Recommended operating conditions Item Symbol Supply voltage Operating temperature Data hold voltage data hold time Operation recovery time 3. Frequency characteristics and current consumption characteristics Item Symbol Frequency tolerance...
  • Page 8: Switching Characteristics (Ac Characteristics)

    RTC - 72421 / 72423 Switching characteristics (AC characteristics) 1. When ALE is used Write mode Item CS1 set-up time Address set-up time before ALE Address hold time after ALE ALE pulse width ALE set-up time before write Write pulse width ALE set-up time after write Data input set-up time before write Data input hold time after write...
  • Page 9: When Ale Is Fixed At

    RTC - 72421 / 72423 2. When ALE is fixed at V Write mode Item CS1 set-up time CS1 hold time Address set-up time before write Address hold time after write Write pulse width Data input set-up time before write Data input hold time after write Write recovery time Read mode...
  • Page 10: Registers

    MASK 0 to it to enable these modes. 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 TEST set to 0 during power-on initialization.
  • Page 11: Setting The Fixed-Period Pulse Output Mode And Fixed-Period Interrupt Mode

    RTC - 72421 / 72423 4. Setting the fixed-period pulse output mode and fixed-period interrupt mode Mode MASK ITRPT/STND Fixed-period pulse output mode Fixed-period interrupt mode Fixed-period pulse output inhibited 5. Resetting the fixed-period pulse output mode and fixed-period interrupt mode Mode Fixed-period pulse output mode MASK=0...
  • Page 12: Register Description

    M10 and M1 registers is 30, this time should be read as 11:30 a.m. When the 12-hour clock is used, the h20 bit should never be 1, but it is nonetheless physically possible to write a 1 in this bit.
  • Page 13: Cd Register (Control Register D)

    RTC - 72421 / 72423 2. CD register (control register D) (1) HOLD bit (D0) Use the HOLD bit when accessing the S1 and W registers. For details, see "Read/write of S1 to W registers". HOLD bit The BUSY status can be checked. When the HOLD bits is 1 and the BUSY bit is 0, read and write are enabled. When the HOLD bit is 1, any incrementation in the count is held within the RTC.
  • Page 14: Ce Register (Control Register E)

    RTC - 72421 / 72423 *STD.P pin output IRQ FLAG 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 15 RTC - 72421 / 72423 2.Fixed-period interrupt mode (ITRPT/STND=1) MASK bit IRQ FLAG bit *STD. P pin The output levels of the STD.P pin are low(down) and open circuit(up). (2) ITRPT/STND bit (D1) The ITRPT/STND bit specifies fixed-period pulse output mode or fixed-period interrupt mode for the fixed-period operating mode.
  • Page 16: Cf Register (Control Register F)

    24/12 bit. (4) TEST bit (D3) 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 17: 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. Power On Start the counter Initialize the control registers...
  • Page 18 RTC - 72421 / 72423 (A)Starting the count START Set the C register Reg.F 0*00B TEST 24/12 0 or 1 STOP RESET Set the C register This setting is not necessary when the STD.P pin is not used Set the C register Reg.D 0*00B...
  • Page 19: Read/Write Of S1 To W Registers

    RTC - 72421 / 72423 2. Read/write of S1 to W registers Use one of the procedures shown below to access registers other than the control registers (CD, CE, and CF) while the RTC is operating. Note that the control registers can be accessed regardless of the status of the BUSY bit. Read or write when the HOLD bit is used From previous process HOLD bit...
  • Page 20: Using The Cs Pin

    RTC - 72421 / 72423 4. Using the CS The RTC-72421/RTC-72423 has 2 chip-select signal systems: CS is not only used for CPU bus control, it also has the main function of switching between standby mode and operating mode. (1) Functions Providing the CS pin with the rated voltage levels enables CS Enabling interface with microprocessor during operation within the operating voltage range (5.0 V 0.5 V)
  • Page 21: 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 8085/MCS48,51 Upper address bus Decoder IO/M The resistors on the RD and WR lines are not necessary if the CPU does not have a HALT or HOLD state.
  • Page 22: External Dimensions

    Marking layout Type RTC72421 EPSON Logo mark 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 23: Reference Data

    = ( 1 / °C ( C ) ( C ) +100 2. To determine overall clock accuracy, add the frequency precision and voltage characteristics. f/f = f/fo + f/fo 3. How to find the date difference...
  • Page 24: Application Notes

    RTC - 72421 / 72423 Application notes 1. Notes on handling This module uses a C-MOS IC to realize low power consumption. Carefully note the following cautions when handling. (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 25 EPSON HONG KONG LTD. 20/F., Harbour Centre, 25 Harbour Road, Wanchai, Hong kong Phone: (852) 2585-4600 Fax: (852) 2827-2152 EPSON ELECTRONIC TECHNOLOGY DEVELOPMENT (SHENZHEN )CO., LTD. Flat 16A, 16/F, New Times Plaza, No.1 Taizi Road, Shenzhen, China Phone EPSON TAIWAN TECHNOLOGY & TRADING LTD.

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Rtc-72423 aRtc-72421 b