Replacing the X1226, X1227, X1228 or X1288 RTC with the ISL12026, ISL12027, ISL12028 ® Application Note 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 for pin compatible and include enhancements over an older family of devices (the “X122x” family). These enhancements include: • 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 Application note 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 The ISL12026 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 can drop into an X1226 socket with no hardware changes required, but certain changes to the battery switchover and battery operation should be reviewed. See the ISL12026 data sheet for more details. April 13, 2007 AN1303.0 operation should be reviewed. See the ISL12027 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. 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 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. The ISL12028 is an RTC device with 4k of EEPROM and includes a FOUT/IRQ 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. Note that there are additional status and control bits added to the registers of the ISL12026. Review their function thoroughly before substituting the ISL12026 for the X1226. Table 1 lists the complete hardware and register changes. If the additional functionality is not needed, however, the ISL12026 default factory setting emulates the older device functionality. 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. Replacing the X1227 with the ISL12027 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. 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 1 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. 2007. All Rights Reserved All other trademarks mentioned are the property of their respective owners. Application Note 1303 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 FOUT/IRQ 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 (such as a microcontroller using a 32kHz clock). Replacing the X1288 with the ISL12028 The X1288 device is the only device in the original RTC product line that contained 256k bits of EEPROM. Two packages are available for the X1288, a 16 Ld SOIC and a 14 Ld TSSOP. The ISL12028 in 14 Ld TSSOP can drop into the X1288 14 Ld TSSOP 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. The ISL12028 is not offered in 16 Ld SOIC package, so there is no new solution that drops into that pinout. The ISL12028 is an RTC device with 4k of EEPROM and includes a FOUT/IRQ 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 X1288 device would not issue a Reset with a stopped oscillator. 2 The major difference between the two parts is that the X1288 has 256k bits of EEPROM general purpose memory, and the ISL12028 has only 4k bits. If the deeper memory is still required when replacing the X1288 part with the ISL12028, then a separate serial I2C EEPROM device will be needed. The 24C256 device is available in an 8 Ld TSSOP from multiple manufacturers. Note that the external EEPROM device will need to have a different slave address from the ISL12028, which is set to 1010111x (where x is the Read/Write bit). There are two other changes that affect microcode or software. First, if the 4k of general purpose EEPROM is used, the memory page size changes from 128 bytes to 16 bytes and 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 is an additional status bit and control register added to the ISL12028, and their function should be reviewed as well. Table 4 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. 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 FOUT/IRQ pin instead of the CMOS output pin found on the ISL12028. This change will reduce battery current drain in applications where the circuitry that connects to this pin is powered down in battery backup mode (such as a microcontroller using a 32kHz clock). AN1303.0 April 13, 2007 Application Note 1303 TABLE 1. REPLACING THE X1226 WITH THE ISL12026 FUNCTION OLD X1226 AFFECTS SOFTWARE? NEW ISL12026 Battery Switchover Devices Switches to Battery Mode Once VCC < VBAT NO Device Switches to Battery when: 1) VCC < VBAT AND 2) VCC < VTRIP with Option to Work the Old Way (called "LP Mode") Battery Switchover Hysteresis on VDD negative transition only in legacy mode Hysteresis on both VDD negative and Positive transitions NO 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 I2C operation with battery Device could work in battery backup as long as VBAT > VTRIP and VBAT > VCC Selectable operation whether I2C is active in battery backup, or will not be active if VBAT > VDD 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 Bits additional functionality RTC Registers Byte write or page write Page write ONLY YES Alarm Function Only Alarm0 (ALM0x) would trigger an IRQ transition Both alarms will trigger IRQ if they are set to different times NO Pin Names PHZ/IRQ 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 NO 3 AN1303.0 April 13, 2007 Application Note 1303 TABLE 2. REPLACING THE X1227 WITH THE ISL12027 FUNCTION OLD X1227 AFFECTS SOFTWARE? NEW ISL12027 Battery Switchover Devices Switches to Battery Mode Once VCC < VBAT NO Device Switches to Battery when: 1) VCC < VBAT AND 2) VCC < VTRIP with Option to Work the Old Way (called "LP Mode") Battery Switchover Hysteresis on VDD negative transition only in legacy mode Hysteresis on both VDD negative and Positive transitions NO 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 (more accurate bandgap) NO Reset Trip Voltages Thresholds adjusted using complicated analog voltage setting procedure Thresholds programmed (1 of 5) using EEPROM register NO 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 Bits additional functionality RTC Registers Byte write or page write Page write ONLY - No single byte writes to setup YES RTC registers Alarm Function Only Alarm0 (ALM0x) would trigger an IRQ transition Both alarms will trigger IRQ if they are set to different times NO Pin Names VBACK VBAT NO Pin Names VCC VDD NO Clock Inputs External Clocking on X1 with special input No External clocking NO 4 AN1303.0 April 13, 2007 Application Note 1303 TABLE 3. REPLACING THE X1228 WITH THE ISL12028 FUNCTION OLD X1228 AFFECTS SOFTWARE? NEW ISL12028 Battery Switchover Devices Switches to Battery Mode Once VCC < VBAT NO Device Switches to Battery when: 1) VCC < VBAT AND 2) VCC < VTRIP with Option to Work the Old Way (called "LP Mode") Battery Switchover Hysteresis on VDD negative transition only in legacy mode Hysteresis on both VDD negative and Positive transitions NO 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 (more accurate bandgap) NO Reset Trip Voltages Thresholds adjusted using complicated analog voltage setting procedure Thresholds programmed (1 of 5) using EEPROM register NO 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 Bits additional functionality RTC Registers Byte write or page write Page write ONLY - No single byte writes to setup YES RTC registers Alarm Function Only Alarm0 (ALM0x) would trigger an IRQ transition Both alarms will trigger IRQ if they are set to different times NO Pin Names PHZ/IRQ FOUT/IRQ NO Pin Names VBACK VBAT NO Pin Names VCC VDD NO Clock Inputs External Clocking on X1 with special input No External clocking NO 5 AN1303.0 April 13, 2007 Application Note 1303 TABLE 4. REPLACING THE X1288 WITH THE ISL12028 FUNCTION OLD X1288 AFFECTS SOFTWARE? NEW ISL12028 Battery Switchover Devices Switches to Battery Mode Once VCC < VBAT NO Device Switches to Battery when: 1) VCC < VBAT AND 2) VCC < VTRIP with Option to Work the Old Way (called "LP Mode") Battery Switchover Hysteresis on VDD negative transition only in legacy mode Hysteresis on both VDD negative and Positive transitions NO 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 (more accurate bandgap) NO Reset Trip Voltages Thresholds adjusted using complicated analog voltage setting procedure Thresholds programmed (1 of 5) using EEPROM register NO 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 32k x 8 size 512 x 8 size YES EEPROM 128-byte Page Write 16-byte Page Write YES Status Register No Oscillator Stopped Bit Status Bit to Indicate Oscillator Stopped NO - optional additional functionality Control Register Legacy switchover only BSW Mode bit to change from Legacy to Standard mode for battery switchover NO - optional additional functionality Control Registers No PWR register Memory Map to Expand to include one more NO - optional Register, at address 014h the PWR register. additional Adds VTRIP selection and battery mode control. functionality RTC Registers Byte write or page write Page write ONLY - No single byte writes to setup YES RTC registers Alarm Function Only Alarm0 (ALM0x) would trigger an IRQ transition Both alarms will trigger IRQ if they are set to different times NO Pin Names PHZ/IRQ (no change) FOUT/IRQ NO Pin Names VBACK (no change) VBAT NO Pin Names VCC (no change) VDD NO Clock Inputs External Clocking on X1 with special input No External clocking 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 6 AN1303.0 April 13, 2007