AN1303: Replacing the X1226, X1227, X1228 or X1288 RTC with the ISL12026, ISL12027, ISL12028

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.
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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
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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
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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
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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
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