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New Features
Repetitive Alarms &
Temperature Compensation
4K (512 x 8)
X1227
2-WireRTC
Real Time Clock/Calendar/CPU Supervisor with EEPROM
FEATURES
• Real Time Clock/Calendar
— Tracks time in Hours, Minutes, and Seconds
— Day of the Week, Day, Month, and Year
• 2 Polled Alarms (Non-volatile)
— Settable on the Second, Minute, Hour, Day of the
Week, Day, or Month
— Repeat Mode (periodic interrupts)
• Oscillator Compensation on chip
— Internal feedback resistor and compensation
capacitors
— 64 position Digitally Controlled Trim Capacitor
— 6 digital frequency adjustment settings to ±30ppm
• CPU Supervisor Functions
— Power On Reset, Low Voltage Sense
— Watchdog Timer (SW Selectable: 0.25s, 0.75s,
1.75s, off)
• Battery Switch or Super Cap Input
• 4K x 8 Bits of EEPROM
— 64-Byte Page Write Mode
— 8 modes of Block Lock™ Protection
— Single Byte Write Capability
• High Reliability
— Data Retention: 100 years
— Endurance: 100,000 cycles per byte
• 2-Wire™ Interface interoperable with I2C*
— 400kHz data transfer rate
• Low Power CMOS
— 1.25µA Operating Current (Typical)
• Small Package Options
— 8-Lead SOIC and 8-Lead TSSOP
APPLICATIONS
• Utility Meters
• HVAC Equipment
• Audio / Video Components
• Set Top Box / Television
• Modems
• Network Routers, Hubs, Switches, Bridges
• Cellular Infrastructure Equipment
• Fixed Broadband Wireless Equipment
• Pagers / PDA
• POS Equipment
• Test Meters / Fixtures
• Office Automation (Copiers, Fax)
• Home Appliances
• Computer Products
• Other Industrial / Medical / Automotive
DESCRIPTION
The X1227 device is a Real Time Clock with clock/
calendar, two polled alarms with integrated 512x8
EEPROM, oscillator compensation, CPU Supervisor
(POR/LVS and WDT) and battery backup switch.
The oscillator uses an external, low-cost 32.768kHz
crystal. All compensation and trim components are
integrated on the chip. This eliminates several external
discrete components and a trim capacitor, saving
board area and component cost.
BLOCK DIAGRAM
32.768kHz
X1
X2
OSC
Compensation
Oscillator
Frequency 1Hz
Divider
Timer
Calendar
Logic
Time
Keeping
Registers
(SRAM)
Battery
Switch
Circuitry
VCC
VBACK
SCL
SDA
Serial
Interface
Decoder
RESET
Control
Decode
Logic
8
Control/
Registers
(EEPROM)
Status
Registers
(SRAM)
Alarm
Watchdog
Timer
Low Voltage
Reset
Compare
Alarm Regs
(EEPROM)
4K
EEPROM
ARRAY
*I2C is a Trademark of Philips.
REV 1.1.20 1/13/03
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X1227
DESCRIPTION (continued)
The Real-Time Clock keeps track of time with separate
registers for Hours, Minutes, Seconds. The Calendar
has separate registers for Date, Month, Year and Day-
of-week. The calendar is correct through 2099, with
automatic leap year correction.
The powerful Dual Alarms can be set to any Clock/
Calendar value for a match. For instance, every
minute, every Tuesday, or 5:23 AM on March 21. The
alarms can be polled in the Status Register. There is a
repeat mode for the alarms allowing a periodic
interrupt.
The X1227 device integrates CPU Supervisor func-
tions and a Battery Switch. There is a Power-On Reset
(RESET output) with typically 250 ms delay from power
on. It will also assert RESET when Vcc goes below the
specified threshold. The Vtrip threshold is user repro-
grammable. There is a WatchDog Timer (WDT) with 3
selectable time-out periods (0.25s, 0.75s, 1.75s) and a
disabled setting. The watchdog activates the RESET
pin when it expires.
The device offers a backup power input pin. This
VBACK pin allows the device to be backed up by battery
or SuperCap. The entire X1227 device is fully
operational from 2.7 to 5.5 volts and the clock/calendar
portion of the X1227 device remains fully operational
down to 1.8 volts (Standby Mode).
The X1227 device provides 4K bits of EEPROM with 8
modes of BlockLock™ control. The BlockLock allows a
safe, secure memory for critical user and configuration
data, while allowing a large user storage area.
PIN DESCRIPTIONS
X1
X2
RESET
VSS
X1227
8-Pin SOIC
18
27
36
45
VCC
VBACK
SCL
SDA
VBACK
VCC
X1
X2
X1227
8-Pin TSSOP
18
27
36
45
SCL
SDA
VSS
RESET
NC = No internal connection
Serial Clock (SCL)
The SCL input is used to clock all data into and out of
the device. The input buffer on this pin is always active
(not gated).
Serial Data (SDA)
SDA is a bidirectional pin used to transfer data into and
out of the device. It has an open drain output and may
be wire ORed with other open drain or open collector
outputs. The input buffer is always active (not gated).
An open drain output requires the use of a pull-up
resistor. The output circuitry controls the fall time of the
output signal with the use of a slope controlled pull-
down. The circuit is designed for 400kHz 2-wire inter-
face speeds.
VBACK
This input provides a backup supply voltage to the
device. VBACK supplies power to the device in the
event the VCC supply fails. This pin can be connected
to a battery, a Supercap or tied to ground if not used.
RESET Output – RESET
This is a reset signal output. This signal notifies a host
processor that the watchdog time period has expired or
that the voltage has dropped below a fixed VTRIP thresh-
old. It is an open drain active LOW output. Recom-
mended value for the pullup resistor is 5K Ohms. If
unused, tie to ground.
X1, X2
The X1 and X2 pins are the input and output,
respectively, of an inverting amplifier. An external
32.768kHz quartz crystal is used with the X1227 to
supply a timebase for the real time clock. The
recommended crystal is a Citizen CFS206-32.768KDZF.
Internal compensation circuitry is included to form a
complete oscillator circuit. Care should be taken in the
placement of the crystal and the layout of the circuit.
Plenty of ground plane around the device and short
traces to X1 and X2 are highly recommended. See
Application section for more recommendations.
Figure 1. Recommended Crystal connection
X1
X2
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X1227
POWER CONTROL OPERATION
The power control circuit accepts a VCC and a VBACK
input. The power control circuit powers the device from
VBACK when VCC < VBACK - 0.2V. It will switch back to
power the device from VCC when VCC exceeds VBACK.
Figure 2. Power Control
VBACK
VCC
Off
Voltage
On
In
REAL TIME CLOCK OPERATION
The Real Time Clock (RTC) uses an external
32.768kHz quartz crystal to maintain an accurate
internal representation of the second, minute, hour,
day, date, month, and year. The RTC has leap-year
correction. The clock also corrects for months having
fewer than 31 days and has a bit that controls 24 hour
or AM/PM format. When the X1227 powers up after
the loss of both VCC and VBACK, the clock will not
operate until at least one byte is written to the clock
register.
Reading the Real Time Clock
The RTC is read by initiating a Read command and
specifying the address corresponding to the register of
the Real Time Clock. The RTC Registers can then be
read in a Sequential Read Mode. Since the clock runs
continuously and a read takes a finite amount of time,
there is the possibility that the clock could change during
the course of a read operation. In this device, the time is
latched by the read command (falling edge of the clock
on the ACK bit prior to RTC data output) into a separate
latch to avoid time changes during the read operation.
The clock continues to run. Alarms occurring during a
read are unaffected by the read operation.
Writing to the Real Time Clock
The time and date may be set by writing to the RTC
registers. To avoid changing the current time by an
uncompleted write operation, the current time value is
loaded into a separate buffer at the falling edge of the
clock on the ACK bit before the RTC data input bytes,
the clock continues to run. The new serial input data
replaces the values in the buffer. This new RTC value
is loaded back into the RTC Register by a stop bit at
the end of a valid write sequence. An invalid write
operation aborts the time update procedure and the
contents of the buffer are discarded. After a valid write
operation the RTC will reflect the newly loaded data
beginning with the next “one second” clock cycle after
the stop bit is written. The RTC continues to update
the time while an RTC register write is in progress and
the RTC continues to run during any nonvolatile write
sequences. A single byte may be written to the RTC
without affecting the other bytes.
Accuracy of the Real Time Clock
The accuracy of the Real Time Clock depends on the
frequency of the quartz crystal that is used as the time
base for the RTC. Since the resonant frequency of a
crystal is temperature dependent, the RTC perfor-
mance will also be dependent upon temperature. The
frequency deviation of the crystal is a fuction of the
turnover temperature of the crystal from the crystal’s
nominal frequency. For example, a >20ppm frequency
deviation translates into an accuracy of >1 minute per
month. These parameters are available from the
crystal manufacturer. Xicor’s RTC family provides on-
chip crystal compensation networks to adjust load-
capacitance to tune oscillator frequency from +116
ppm to –37 ppm when using a 12.5 pF load crystal.
For more detail information see the Application
section.
CLOCK/CONTROL REGISTERS (CCR)
The Control/Clock Registers are located in an area
separate from the EEPROM array and are only
accessible following a slave byte of “1101111x” and
reads or writes to addresses [0000h:003Fh]. The
clock/control memory map has memory addresses
from 0000h to 003Fh. The defined addresses are
described in the Table 1. Writing to and reading from
the undefined addresses are not recommended.
CCR access
The contents of the CCR can be modified by perform-
ing a byte or a page write operation directly to any
address in the CCR. Prior to writing to the CCR
(except the status register), however, the WEL and
RWEL bits must be set using a two step process (See
section “Writing to the Clock/Control Registers.”)
The CCR is divided into 5 sections. These are:
1. Alarm 0 (8 bytes; non-volatile)
2. Alarm 1 (8 bytes; non-volatile)
3. Control (4 bytes; non-volatile)
4. Real Time Clock (8 bytes; volatile)
5. Status (1 byte; volatile)
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