Replacing the x1226, x1227 or x1228 RTC with the ISL12026, ISL12026A, ISL12027 or ISL12028 ® Technical Brief December 4, 2008 TB460.1 Introduction Replacing the x1227 with the ISL12027 Intersil has recently introduced a new family of Real Time Clock (RTC) devices (the “ISL1202x” family), which include 4k of EEPROM. These devices are pin-to-pin compatible and include enhancements over an older family of devices (the “x122x” family). These enhancements include: The ISL12027 is an RTC device with 4k of EEPROM and includes a RESET pin for outputting a hardware Reset signal for microcontroller or logic system reset, or a watchdog timer reset. The Reset function was improved in the ISL12027 to perform a Reset even if the oscillator has not started or has been stopped. The x1227 device would not issue a Reset with a stopped oscillator. The ISL12027 can drop into an x1227 socket with no hardware changes required, but certain changes to the battery switchover and battery operation should be reviewed. See the ISL12027 data sheet for more details. • Lower supply and battery backup current • Reliable battery switchover • Accurate Reset voltage trip points • Oscillator functionality detection Other enhancements are detailed in the data sheets. This Technical Brief provides information for an engineer wishing to use the new devices to replace the older devices in their system. Replacing the x1226 with the ISL12026 and ISL12026A The ISL12026, ISL12026A is an RTC device with 4k of EEPROM and includes an IRQ/FOUT pin for outputting an alarm interrupt or constant frequency clock. The ISL12026, ISL12026A can drop into an x1226 socket with no hardware changes required, but certain changes to the battery switchover and battery operation should be reviewed. Note that the ISL12026 cannot drop into applications where normal operation requires VBAT>VDD (such as when VDD = 3.0V and VBAT = 3.2V).The default register setup only allows reading registers using the I2C bus with VBAT>VDD, not writing. For full I2C read and write operation with VBAT>VDD, the ISL12026A is available with the correct default setting for this operation. There are only two changes that affect microcode or software. First, the change in general purpose EEPROM memory page size from 64 bytes to 16 bytes will require changes to the memory writing procedure. Second, the RTC registers require a full page write at a time instead of allowing a single byte write. A single byte write to the RTC registers will result in no update to those registers at all. Note that there are additional status and control bits added to the registers of the ISL12026 and ISL12026A. Review their function thoroughly before substituting the ISL12026 or ISL12026A for the x1226. Table 1 lists the complete hardware and register changes. If the additional functionality is not needed, however, the ISL12026A default factory setting emulates the older device functionality. 1 There are only two changes that affect microcode or software. First, the change in general purpose EEPROM memory page size from 64 bytes to 16 bytes will require changes to the memory writing procedure. Second, the RTC registers require a full page write at a time instead of allowing a single byte write. A single byte write to the RTC registers will result in no update to those registers at all. Note that there are additional status and control bits added to the registers of the ISL12027, and their function should be reviewed as well. Review their function thoroughly before substituting the ISL12027 for the x1227. Table 2 lists the complete hardware and register changes. If the additional functionality is not needed, however, the device default setting from the factory emulates the older device functionality. Replacing the x1228 with the ISL12028 The ISL12028 is an RTC device with 4k of EEPROM and includes an IRQ/FOUT pin for outputting an alarm interrupt or constant frequency clock, and a RESET pin for outputting a hardware Reset signal for microcontroller or logic system reset or a watchdog timer reset. The Reset function was improved in the ISL12028 to perform a Reset even if the oscillator has not started or has been stopped. The x1228 device would not issue a Reset with a stopped oscillator. The ISL12028 can drop into an x1228 socket with no hardware changes required, but certain changes to the battery switchover and battery operation should be reviewed. See the ISL12028 data sheet for more details. There are only two changes that affect microcode or software. First, the change in general purpose EEPROM memory page size from 64 bytes to 16 bytes will require changes to the memory writing procedure. Second, the RTC registers require a full page write at a time instead of allowing a single byte write. A single byte write to the RTC registers will result in no update to those registers at all. CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2006, 2008. All Rights Reserved All other trademarks mentioned are the property of their respective owners. Technical Brief 460 Note that the ISL12029 device has been introduced as well, and is the same as the ISL12028 in all respects except for an open drain IRQ/FOUT pin instead of the CMOS output pin found on the ISL12028. This change will reduce battery current drain in applications where the circuitry that connect to this pin is powered down in battery backup mode. Note that there are additional status and control bits added to the registers of the ISL12027, and their function should be reviewed as well. Review their function thoroughly before substituting the ISL12028 for the x1228. Table 3 lists the complete hardware and register changes. If the additional functionality is not needed, however, the device default setting from the factory emulates the older device functionality. TABLE 1. REPLACING THE x1226 WITH THE ISL12026 AND ISL12026A FUNCTION OLD X1226 NEW ISL12026 or ISL12026A AFFECTS SOFTWARE? Battery Switchover Device switches to battery mode once VCC < VBAT Battery Switchover Hysteresis on VCC negative transition only Hysteresis on both VDD negative and positive NO in legacy mode transitions Battery Current 1.25µA battery backup current 800nA battery backup current NO Power Supply Min rise/fall times for VCC only Max slew rate for VDD NO ISL12026 will NOT allow I2C writes in default Device could work in battery backup as long as VBAT > VTRIP and VBAT > VCC, mode in applications where VBAT > VDD. The including I2C operation with VBAT > VCC. ISL12026A is needed for performing I2C writes with VBAT > VDD. This operation is register selectable NO. Selecting the correct device should not require changing a register setting. EEPROM 64-byte page write 16-byte page write YES Status Register (None) Status bit to indicate oscillator stopped NO - Optional additional functionality Status Register Legacy switchover only BSW mode bit to change from legacy to standard mode for battery switchover NO - Optional additional functionality Control Registers (None) Memory map to expand slightly from addition of NO - Optional additional bits functionality RTC Registers Byte write or page write Page write ONLY YES Pin Names IRQ/PHZ IRQ/FOUT NO Pin Names VBACK VBAT NO Pin Names VCC VDD NO Clock Inputs External clocking on X1 with special input No external clocking I2C Operation with VBAT>VDD 2 Default mode is called "LP Mode" whereby the NO device switches to battery when VDD<VBAT. An option exists called “Normal Mode” which requires 1) VCC < VBAT AND 2) VCC < VTRIP. NO TB460.1 December 4, 2008 Technical Brief 460 TABLE 2. REPLACING THE x1227 WITH THE ISL12027 FUNCTION OLD X1227 NEW ISL12027 AFFECTS SOFTWARE? Battery Switchover Device switches to battery mode once VCC Device switches to battery when 1) VCC < VBAT NO < VBAT AND 2) VCC < VRESET with option to work the old way (called "LP Mode") Battery Switchover Hysteresis on VDD negative transition only Hysteresis on both VDD negative and positive NO in legacy mode transitions Battery Current 1.25µA battery backup current 800nA battery backup current NO Power Supply Min rise/fall times for VCC only Max slew rate for VDD NO Reset Trip Voltages 4 available reset thresholds with ±2.5% accuracy (old floating gate reference) 5 available reset thresholds with ±1.5% accuracy NO (more accurate bandgap) Reset Trip Voltages Thresholds adjusted using complicated analog voltage setting procedure Thresholds programmed (1 of 5) using EEPROM NO register I2C Operation with Battery Device could work as long as VBAT > VDD > VRESET Selectable operation whether I2C is active in battery backup NO Operation with NO Oscillator No reset, no I2C communication Reset will occur with no battery, I2C can communicate NO EEPROM 64-byte page write 16-byte page write YES Status Register (None) Status bit to indicate oscillator stopped NO - Optional additional functionality Status Register Legacy switchover only BSW mode bit to change from legacy to standard mode for battery switchover NO - Optional additional functionality Control Registers (None) Memory map to expand slightly from addition of NO - Optional additional bits functionality RTC Registers Byte write or page write Page write ONLY - No single byte writes to setup YES RTC registers Pin Names VBACK VBAT NO Pin Names VCC VDD NO Clock Inputs External clocking on X1 with special input No external clocking 3 NO TB460.1 December 4, 2008 Technical Brief 460 TABLE 3. REPLACING THE X1228 WITH THE ISL12028 FUNCTION OLD X1228 NEW ISL12028 AFFECTS SOFTWARE? Battery Switchover Device switches to battery mode once VCC < VBAT Battery Switchover Hysteresis on VDD negative transition only Hysteresis on both VDD negative and positive NO in legacy mode transitions Battery Current 1.25µA battery backup current 800nA battery backup current NO Power Supply Min rise/fall times for VCC only Max slew rate for VDD NO Reset Trip Voltages 4 available reset thresholds with ±2.5% accuracy (old floating gate reference) 5 available reset thresholds with ±1.5% accuracy NO (more accurate bandgap) Reset Trip Voltages Thresholds adjusted using complicated analog voltage setting procedure Thresholds programmed (1 of 5) using EEPROM NO register I2C Operation with Battery Device could work as long as VBAT > VDD > VRESET Selectable operation whether I2C is active in battery backup NO Operation with NO Oscillator No reset, no I2C communication Reset will occur with no battery, I2C can communicate NO EEPROM 64-byte page write 16-byte page write YES Status Register (None) Status bit to indicate oscillator stopped NO - Optional additional functionality Status Register Legacy switchover only BSW mode bit to change from legacy to standard mode for battery switchover NO - Optional additional functionality Control Registers (None) Memory map to expand slightly from addition of NO - Optional additional bits functionality RTC Registers Byte write or page write Page write ONLY - No single byte writes to setup YES RTC registers Pin Names IRQ/PHZ IRQ/FOUT NO Pin Names VBACK VBAT NO Pin Names VCC VDD NO Clock Inputs External clocking on X1 with special input No external clocking Device switches to battery when 1) VCC < VBAT NO AND 2) VCC < VRESET with option to work the old way (called "LP Mode") NO Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that the Application Note or Technical Brief is current before proceeding. For information regarding Intersil Corporation and its products, see www.intersil.com 4 TB460.1 December 4, 2008