X1227S8I-4.5A - Xicor, Inc. - Datasheet.Directory

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Characteristics subject to change without notice.

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4K (512 x 8)

2-Wire

™

RTC

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.

X1227

BLOCK DIAGRAM

Oscillator Frequency Timer

Logic

Divider Calendar

Control/

Registers

1Hz Time

Keeping

Registers

Alarm Regs

Compare

Mask

RESET

Control

Decode

Logic

Alarm

(EEPROM)

SCL

SDA

Serial

Interface

Decoder

EEPROM

ARRAY

Watchdog

Timer

Low Voltage

Reset

Registers

Status

(SRAM)

VCC

VBACK

32.768kHz

(SRAM)

Battery

Circuitry

Switch

OSC

Compensation

*I2C is a Trademark of Philips.

New Features

Repetitive Alarms &

Temperature Compensation

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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 V

trip

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

BACK

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

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.

BACK

This input provides a backup supply voltage to the

device. V

BACK

supplies power to the device in the

event the V

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 V

TRIP

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

NC = No internal connection

X1227

VBACK

VCC

RESET

SCL

SDA

VSS

8-Pin TSSOP

X1227

X2 VBACK

VCC

RESET SCL

SDA

VSS

8-Pin SOIC

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POWER CONTROL OPERATION

The power control circuit accepts a V

and a V

BACK

input. The power control circuit powers the device from

BACK

when V

< V

BACK

- 0.2V. It will switch back to

power the device from V

when V

exceeds V

BACK

Figure 2. Power Control

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 V

and V

BACK

, the clock will not

operate until at least one byte is written to the clock

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)

VBACK In

Voltage

VCC

Off

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Table 1. Clock/Control Memory Map

Addr. Type Reg

Name

Bit

Range

Default

76543210

(optional)

003F Status SR BAT AL1 AL0 0 0 RWEL WEL RTCF 01h

0037 RTC

(SRAM)

Y2K 0 0 Y2K21 Y2K20 Y2K13 0 0 Y2K10 19/20 20h

0036 DW 0 0 0 0 0 DY2 DY1 DY0 0-6 00h

0035 YR Y23 Y22 Y21 Y20 Y13 Y12 Y11 Y10 0-99 00h

0034 MO 0 0 0 G20 G13 G12 G11 G10 1-12 00h

0033 DT 0 0 D21 D20 D13 D12 D11 D10 1-31 00h

0032 HR MIL 0 H21 H20 H13 H12 H11 H10 0-23 00h

0031 MN 0 M22 M21 M20 M13 M12 M11 M10 0-59 00h

0030 SC 0 S22 S21 S20 S13 S12 S11 S10 0-59 00h

0013 Control

(EEPROM)

DTR 0 0 0 0 0 DTR2 DTR1 DTR0 00h

0012 ATR 0 0 ATR5 ATR4 ATR3 ATR2 ATR1 ATR0 00h

0011 INT Unused

0010 BL BP2 BP1 BP0 WD1 WD0 0 0 0 00h

000F Alarm1

(EEPROM)

Y2K1 0 0 A1Y2K21 A1Y2K20 A1Y2K13 0 0 A1Y2K10 19/20 20h

000E DWA1 EDW1 0 0 0 0 DY2 DY1 DY0 0-6 00h

000D YRA1 Unused - Default = RTC Year value (No EEPROM) - Future expansion

000C MOA1 EMO1 0 0 A1G20 A1G13 A1G12 A1G11 A1G10 1-12 00h

000B DTA1 EDT1 0 A1D21 A1D20 A1D13 A1D12 A1D11 A1D10 1-31 00h

000A HRA1 EHR1 0 A1H21 A1H20 A1H13 A1H12 A1H11 A1H10 0-23 00h

0009 MNA1 EMN1 A1M22 A1M21 A1M20 A1M13 A1M12 A1M11 A1M10 0-59 00h

0008 SCA1 ESC1 A1S22 A1S21 A1S20 A1S13 A1S12 A1S11 A1S10 0-59 00h

0007 Alarm0

(EEPROM)

Y2K0 0 0 A0Y2K21 A0Y2K20 A0Y2K13 0 0 A0Y2K10 19/20 20h

0006 DWA0 EDW0 0 0 0 0 DY2 DY1 DY0 0-6 00h

0005 YRA0 Unused - Default = RTC Year value (No EEPROM) - Future expansion

0004 MOA0 EMO0 0 0 A0G20 A0G13 A0G12 A0G11 A0G10 1-12 00h

0003 DTA0 EDT0 0 A0D21 A0D20 A0D13 A0D12 A0D11 A0D10 1-31 00h

0002 HRA0 EHR0 0 A0H21 A0H20 A0H13 A0H12 A0H11 A0H10 0-23 00h

0001 MNA0 EMN0 A0M22 A0M21 A0M20 A0M13 A0M12 A0M11 A0M10 0-59 00h

0000 SCA0 ESC0 A0S22 A0S21 A0S20 A0S13 A0S12 A0S11 A0S10 0-59 00h

Each register is read and written through buffers. The

non-volatile portion (or the counter portion of the RTC) is

updated only if RWEL is set and only after a valid write

operation and stop bit. A sequential read or page write

operation provides access to the contents of only one

section of the CCR per operation. Access to another sec-

tion requires a new operation. Continued reads or writes,

once reaching the end of a section, will wrap around to

the start of the section. A read or write can begin at any

address in the CCR.

It is not necessary to set the RWEL bit prior to writing

the status register. Section 5 supports a single byte

read or write only. Continued reads or writes from this

section terminates the operation.

The state of the CCR can be read by performing a ran-

dom read at any address in the CCR at any time. This

returns the contents of that register location. Addi-

tional registers are read by performing a sequential

read. The read instruction latches all Clock registers

into a buffer, so an update of the clock does not

change the time being read. A sequential read of the

CCR will not result in the output of data from the mem-

ory array. At the end of a read, the master supplies a

stop condition to end the operation and free the bus.

After a read of the CCR, the address remains at the

previous address +1 so the user can execute a current

address read of the CCR and continue reading the

next Register.

ALARM REGISTERS

There are two alarm registers whose contents mimic the

contents of the RTC register, but add enable bits and

exclude the 24 hour time selection bit. The enable bits

specify which registers to use in the comparison between

the Alarm and Real Time Registers. For example:

– Setting the Enable Month bit (EMOn*) bit in combi-

nation with other enable bits and a speciﬁc alarm

time, the user can establish an alarm that triggers at

the same time once a year.

– *n = 0 for Alarm 0: N = 1 for Alarm 1

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When there is a match, an alarm ﬂag is set. The occur-

rence of an alarm can be determined by polling the

AL0 and AL1 bits or by enabling the IRQ output, using

it as hardware ﬂag.

The alarm enable bits are located in the MSB of the

particular register. When all enable bits are set to ‘0’,

there are no alarms.

– The user can set the X1227 to alarm every Wednes-

day at 8:00 AM by setting the EDWn*, the EHRn*

and EMNn* enable bits to ‘1’ and setting the DWAn*,

HRAn* and MNAn* Alarm registers to 8:00 AM

Wednesday.

– A daily alarm for 9:30PM results when the EHRn*

and EMNn* enable bits are set to ‘1’ and the HRAn*

and MNAn* registers are set to 9:30 PM.

*n = 0 for Alarm 0: N = 1 for Alarm 1

REAL TIME CLOCK REGISTERS

Clock/Calendar Registers (SC, MN, HR, DT, MO,

YR)

These registers depict BCD representations of the

time. As such, SC (Seconds) and MN (Minutes) range

from 00 to 59, HR (Hour) is 1 to 12 with an AM or PM

indicator (H21 bit) or 0 to 23 (with MIL=1), DT (Date) is

1 to 31, MO (Month) is 1 to 12, YR (Year) is 0 to 99.

Date of the Week Register (DW)

This register provides a Day of the Week status and

uses three bits DY2 to DY0 to represent the seven

days of the week. The counter advances in the cycle

0-1-2-3-4-5-6-0-1-2-… The assignment of a numerical

value to a speciﬁc day of the week is arbitrary and may

be decided by the system software designer. The

default value is deﬁned as ‘0’.

24 Hour Time

If the MIL bit of the HR register is 1, the RTC uses a

24-hour format. If the MIL bit is 0, the RTC uses a 12-

hour format and H21 bit functions as an AM/PM indi-

cator with a ‘1’ representing PM. The clock defaults to

standard time with H21=0.

Leap Years

Leap years add the day February 29 and are deﬁned

as those years that are divisible by 4. Years divisible by

100 are not leap years, unless they are also divisible

by 400. This means that the year 2000 is a leap year,

the year 2100 is not. The X1227 does not correct for

the leap year in the year 2100.

STATUS REGISTER (SR)

The Status Register is located in the CCR Memory

Map at address 003Fh. This is a volatile register only

and is used to control the WEL and RWEL write

enable latches, read two power status and two alarm

bits. This register is separate from both the array and

the Clock/Control Registers (CCR).

Table 2. Status Register (SR)

BAT: Battery Supply—Volatile

This bit set to “1” indicates that the device is operating

from V

BACK

, not V

. It is a read-only bit and is set/

reset by hardware (X1227 internally). Once the device

begins operating from V

, the device sets this bit to

“0”.

AL1, AL0: Alarm bits—Volatile

These bits announce if either alarm 0 or alarm 1 match

the real time clock. If there is a match, the respective

bit is set to ‘1’. The falling edge of the last data bit in a

SR Read operation resets the ﬂags. Note: Only the AL

bits that are set when an SR read starts will be reset.

An alarm bit that is set by an alarm occurring during an

SR read operation will remain set after the read opera-

tion is complete.

RWEL: Register Write Enable Latch—Volatile

This bit is a volatile latch that powers up in the LOW

(disabled) state. The RWEL bit must be set to “1” prior

to any writes to the Clock/Control Registers. Writes to

RWEL bit do not cause a nonvolatile write cycle, so the

device is ready for the next operation immediately after

the stop condition. A write to the CCR requires both

the RWEL and WEL bits to be set in a speciﬁc

sequence.

WEL: Write Enable Latch—Volatile

The WEL bit controls the access to the CCR and

memory array during a write operation. This bit is a

volatile latch that powers up in the LOW (disabled)

state. While the WEL bit is LOW, writes to the CCR or

any array address will be ignored (no acknowledge will

be issued after the Data Byte). The WEL bit is set by

writing a “1” to the WEL bit and zeroes to the other bits

of the Status Register. Once set, WEL remains set

until either reset to 0 (by writing a “0” to the WEL bit

and zeroes to the other bits of the Status Register) or

Addr 7 6 5 4 3 2 1 0

003Fh BAT AL1 AL0 0 0 RWEL WEL RTCF

Default 0 0 0 0 0 0 0 1

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until the part powers up again. Writes to WEL bit do

not cause a nonvolatile write cycle, so the device is

ready for the next operation immediately after the stop

condition.

RTCF: Real Time Clock Fail Bit—Volatile

This bit is set to a ‘1’ after a total power failure. This is

a read only bit that is set by hardware (X1227 inter-

nally) when the device powers up after having lost all

power to the device. The bit is set regardless of

whether V

or V

BACK

is applied ﬁrst. The loss of only

one of the supplies does not result in setting the RTCF

bit. The ﬁrst valid write to the RTC after a complete

power failure (writing one byte is sufﬁcient) resets the

RTCF bit to ‘0’.

Unused Bits:

This device does not use bits 3 or 4 in the SR, but

must have a zero in these bit positions. The Data Byte

output during a SR read will contain zeros in these bit

locations.

CONTROL REGISTERS

The Control Bits and Registers, described under this

section, are nonvolatile.

Block Protect Bits—BP2, BP1, BP0

The Block Protect Bits, BP2, BP1 and BP0, determine

which blocks of the array are write protected. A write to a

protected block of memory is ignored. The block protect

bits will prevent write operations to one of eight segments

of the array. The partitions are described in Table 3 .

Table 3. Block Protect Bits

Watchdog Timer Control Bits—WD1, WD0

The bits WD1 and WD0 control the period of the

Watchdog Timer. See Table 4 for options.

Table 4. Watchdog Timer Time-Out Options

ON-CHIP OSCILLATOR COMPENSATION

Digital Trimming Register (DTR) — DTR2, DTR1

and DTR0 (Non-Volatile)

The digital trimming Bits DTR2, DTR1 and DTR0

adjust the number of counts per second and average

the ppm error to achieve better accuracy.

DTR2 is a sign bit. DTR2=0 means frequency

compensation is > 0. DTR2=1 means frequency

compensation is < 0.

DTR1 and DTR0 are scale bits. DTR1 gives 10 ppm

adjustment and DTR0 gives 20 ppm adjustment.

A range from -30ppm to +30ppm can be represented

by using three bits above.

Table 5. Digital Trimming Registers

BP2

BP1

BP0

Protected Addresses

X1227 Array Lock

0 0 0 None (Default) None

001 180

– 1FF

Upper 1/4

010 100

– 1FF

Upper 1/2

011 000

– 1FF

Full Array

100 000

– 03F

First Page

101 000

– 07F

First 2 pgs

110 000

– 0FF

First 4 pgs

111 000

– 1FF

First 8 pgs

WD1 WD0 Watchdog Time-Out Period

0 0 1.75 seconds (Factory Default)

0 1 750 milliseconds

1 0 250 milliseconds

1 1 Disabled

DTR Register Estimated frequency

PPMDTR2 DTR1 DTR0

0 0 0 0 (Default)

0 1 0 +10

0 0 1 +20

0 1 1 +30

100 0

1 1 0 -10

1 0 1 -20

1 1 1 -30

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Analog Trimming Register (ATR) (Non-volatile)

Six analog trimming Bits from

ATR5

ATR0

are pro-

vided to adjust the on-chip loading capacitance range.

The on-chip load capacitance ranges from 3.25pF to

18.75pF. Each bit has a different weight for capaci-

tance adjustment. Using a Citizen CFS-206 crystal

with different ATR bit combinations provides an esti-

mated ppm range from +116ppm to -37ppm to the

nominal frequency compensation. The combination of

digital and analog trimming can give up to +146ppm

adjustment.

The on-chip capacitance can be calculated as follows:

AT R = [(ATR value, decimal) x 0.25pF] + 11.0pF

Note that the ATR values are in two’s complement,

with ATR(000000) = 11.0pF, so the entire range runs

from 3.25pF to 18.75pF in 0.25pF steps.

The values calculated above are typical, and total load

capacitance seen by the crystal will include approxi-

mately 2pF of package and board capacitance in addi-

tion to the ATR value.

See Application section and Xicor’s Application Note

AN154 for more information.

WRITING TO THE CLOCK/CONTROL REGISTERS

Changing any of the nonvolatile bits of the clock/con-

trol register requires the following steps:

– Write a 02h to the Status Register to set the Write

Enable Latch (WEL). This is a volatile operation,

so there is no delay after the write. (Operation

preceeded by a start and ended with a stop).

– Write a 06h to the Status Register to set both the

bit. This is also a volatile cycle. The zeros in the data

byte are required. (Operation preceeded by a start

and ended with a stop).

– Write one to 8 bytes to the Clock/Control Registers

with the desired clock, alarm, or control data. This

sequence starts with a start bit, requires a slave byte

of “11011110” and an address within the CCR and is

terminated by a stop bit. A write to the CCR changes

EEPROM values so these initiate a nonvolatile write

cycle and will take up to 10ms to complete. Writes to

undeﬁned areas have no effect. The RWEL bit is

reset by the completion of a nonvolatile write cycle,

so the sequence must be repeated to again initiate

another change to the CCR contents. If the

sequence is not completed for any reason (by send-

ing an incorrect number of bits or sending a start

instead of a stop, for example) the RWEL bit is not

reset and the device remains in an active mode.

– Writing all zeros to the status register resets both the

WEL and RWEL bits.

– A read operation occurring between any of the

previous operations will not interrupt the register

write operation.

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POWER ON RESET

Application of power to the X1227 activates a Power

On Reset Circuit that pulls the RESET pin active. This

signal provides several beneﬁts.

– It prevents the system microprocessor from starting

to operate with insufﬁcient voltage.

– It prevents the processor from operating prior to sta-

bilization of the oscillator.

– It allows time for an FPGA to download its conﬁgura-

tion prior to initialization of the circuit.

– It prevents communication to the EEPROM, greatly

reducing the likelihood of data corruption on power up.

When VCC exceeds the device VTRIP threshold value

for typically 250ms the circuit releases RESET, allow-

ing the system to begin operation. Recommended slew

rate is between 0.2V/ms and 50V/ms.

WATCHDOG TIMER OPERATION

The watchdog timer is selectable. By writing a value to

WD1 and WD0, the watchdog timer can be set to 3 dif-

ferent time out periods or off. When the Watchdog

timer is set to off, the watchdog circuit is conﬁgured for

low power operation.

Watchdog Timer Restart

The Watchdog Timer is started by a falling edge of

SDA when the SCL line is high and followed by a stop

bit. The start signal restarts the watchdog timer

counter, resetting the period of the counter back to the

maximum. If another start fails to be detected prior to

the watchdog timer expiration, then the RESET pin

becomes active. In the event that the start signal

occurs during a reset time out period, the start will

have no effect. When using a single START to refresh

watchdog timer, a STOP bit should be followed to reset

the device back to stand-by mode.

LOW VOLTAGE RESET OPERATION

When a power failure occurs, and the voltage to the

part drops below a ﬁxed vTRIP voltage, a reset pulse is

issued to the host microcontroller. The circuitry moni-

tors the VCC line with a voltage comparator which

senses a preset threshold voltage. Power up and

power down waveforms are shown in Figure 4. The

Low Voltage Reset circuit is to be designed so the

RESET signal is valid down to 1.0V.

When the low voltage reset signal is active, the operation

of any in progress nonvolatile write cycle is unaffected,

allowing a nonvolatile write to continue as long as possi-

ble (down to the power on reset voltage). The low voltage

reset signal, when active, terminates in progress commu-

nications to the device and prevents new commands, to

reduce the likelihood of data corruption.

Figure 3. Watchdog Restart/Time Out

tRSP<tWDO tRST

RESET

SDA

tRSP

Note: All inputs are ignored during the active reset period (tRST).

tRST

SCL

tRSP>tWDO

Start Stop Start

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Figure 4. Power On Reset and Low Voltage Reset

TRIP

RESET

PURST

RPD

RVALID

VCC THRESHOLD RESET PROCEDURE

[OPTIONAL]

The X1227 is shipped with a standard VCC threshold

(VTRIP) voltage. This value will not change over normal

operating and storage conditions. However, in applica-

tions where the standard VTRIP is not exactly right, or if

higher precision is needed in the VTRIP value, the

X1227 threshold may be adjusted. The procedure is

described below, and uses the application of a nonvol-

atile write control signal.

Setting the VTRIP Voltage

It is necessary to reset the trip point before setting the

new value.

To set the new VTRIP voltage, apply the desired VTRIP

threshold voltage to the VCC pin and tie the RESET pin

to the programming voltage VP

. Then write data 00h to

address 01h. The stop bit following a valid write opera-

tion initiates the VTRIP programming sequence. Bring

RESET to VCC to complete the operation. Note: this

operation may take up to 10 milliseconds to complete

and also writes 00h to address 01h of the EEPROM

array.

Figure 5. Set VTRIP Level Sequence (VCC = desired VTRIP value)

SCL

SDA

01h

RESET VP = 15V

00h

01234567 01234567 01234567 01234567

AEh 00h

VCC

Note: BP0, BP1, BP2 must be disabled.

Resetting the VTRIP Voltage

This procedure is used to set the VTRIP to a “native”

voltage level. For example, if the current VTRIP is 4.4V

and the new VTRIP must be 4.0V, then the VTRIP must

be reset. When VTRIP is reset, the new VTRIP is some-

thing less than 1.7V. This procedure must be used to

set the voltage to a lower value.

To reset the new VTRIP voltage, apply more than 5.5V

to the VCC pin and tie the RESET pin to the

programming voltage VP

. Then write 00h to address

03h. The stop bit of a valid write operation initiates the

VTRIP programming sequence. Bring RESET to VCC to

complete the operation. Note: this operation takes up

to 10 milliseconds to complete and also writes 00h to

address 03h of the EEPROM array.

For best accuracy in setting VTRIP

, it is advised that the

following sequence be used.

1.Program VTRIP as above.

2.Measure resulting VTRIP by measuring the VCC

value where a RESET occurs. Calculate Delta =

(Desired – Measured) VTRIP value.

3.Perform a VTRIP program using the following formula

to set the voltage of the RESET pin:

VRESET = (Desired Value – Delta) + 0.025V

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SERIAL COMMUNICATION

Interface Conventions

The device supports a bidirectional bus oriented proto-

col. The protocol deﬁnes any device that sends data

onto the bus as a transmitter, and the receiving device

as the receiver. The device controlling the transfer is

called the master and the device being controlled is

called the slave. The master always initiates data trans-

fers, and provides the clock for both transmit and

receive operations. Therefore, the devices in this family

operate as slaves in all applications.

Clock and Data

Data states on the SDA line can change only during

SCL LOW. SDA state changes during SCL HIGH are

reserved for indicating start and stop conditions. See

Figure 7.

Start Condition

All commands are preceded by the start condition,

which is a HIGH to LOW transition of SDA when SCL is

HIGH. The device continuously monitors the SDA and

SCL lines for the start condition and will not respond to

any command until this condition has been met. See

Figure 8.

Stop Condition

All communications must be terminated by a stop

condition, which is a LOW to HIGH transition of SDA

when SCL is HIGH. The stop condition is also used to

place the device into the Standby power mode after a

read sequence. A stop condition can only be issued

after the transmitting device has released the bus. See

Figure 8.

Acknowledge

Acknowledge is a software convention used to indicate

successful data transfer. The transmitting device, either

master or slave, will release the bus after transmitting

eight bits. During the ninth clock cycle, the receiver will

pull the SDA line LOW to acknowledge that it received

the eight bits of data. Refer to Figure 9.

The device will respond with an acknowledge after rec-

ognition of a start condition and if the correct Device

Identiﬁer and Select bits are contained in the Slave

Address Byte. If a write operation is selected, the

device will respond with an acknowledge after the

receipt of each subsequent eight bit word. The device

will acknowledge all incoming data and address bytes,

except for:

– The Slave Address Byte when the Device Identiﬁer

and/or Select bits are incorrect

– All Data Bytes of a write when the WEL in the Write

Protect Register is LOW

– The 2nd Data Byte of a Status Register Write Opera-

tion (only 1 data byte is allowed)

In the read mode, the device will transmit eight bits of

data, release the SDA line, then monitor the line for an

acknowledge. If an acknowledge is detected and no

stop condition is generated by the master, the device

will continue to transmit data. The device will terminate

further data transmissions if an acknowledge is not

detected. The master must then issue a stop condition

to return the device to Standby mode and place the

device into a known state.

Figure 6. Reset VTRIP Level Sequence

01234567

SCL

SDA

AEh

01234567

03h

RESET VP = 15V

00h

01234567 01234567

00h

VCC

Note: BP0, BP1, BP2 must be disabled.

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Figure 7. Valid Data Changes on the SDA Bus

Figure 8. Valid Start and Stop Conditions

SCL

SDA

Data Stable Data Change Data Stable

SCL

SDA

Start Stop

Figure 9. Acknowledge Response From Receiver

SCL from

Master

Data Output

from Transmitter

Data Output

from Receiver

81 9

Start Acknowledge

DEVICE ADDRESSING

Following a start condition, the master must output a

Slave Address Byte. The ﬁrst four bits of the Slave

Address Byte specify access to either the EEPROM

array or to the CCR. Slave bits ‘1010’ access the

EEPROM array. Slave bits ‘1101’ access the CCR.

When shipped from the factory, EEPROM array is

UNDEFINED, and should be programmed by the cus-

tomer to a known state.

Bit 3 through Bit 1 of the slave byte specify the device

select bits. These are set to ‘111’.

The last bit of the Slave Address Byte deﬁnes the oper-

ation to be performed. When this R/W bit is a one, then

a read operation is selected. A zero selects a write

operation. Refer to Figure 10.

After loading the entire Slave Address Byte from the

SDA bus, the X1227 compares the device identiﬁer

and device select bits with ‘1010111’ or ‘1101111’.

Upon a correct compare, the device outputs an

acknowledge on the SDA line.

Following the Slave Byte is a two byte word address.

The word address is either supplied by the master

device or obtained from an internal counter. On power

up the internal address counter is set to address 0h, so

a current address read of the EEPROM array starts at

address 0. When required, as part of a random read,

the master must supply the 2 Word Address Bytes as

shown in Figure 10.

In a random read operation, the slave byte in the

“dummy write” portion must match the slave byte in the

“read” section. That is if the random read is from the

array the slave byte must be 1010111x in both

instances. Similarly, for a random read of the Clock/

Control Registers, the slave byte must be 1101111x in

both places.

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Write Operations

Byte Write

For a write operation, the device requires the Slave

Address Byte and the Word Address Bytes. This gives

the master access to any one of the words in the array

or CCR. (Note: Prior to writing to the CCR, the master

must write a 02h, then 06h to the status register in two

preceding operations to enable the write operation.

See “Writing to the Clock/Control Registers.” Upon

receipt of each address byte, the X1227 responds with

an acknowledge. After receiving both address bytes

the X1227 awaits the eight bits of data. After receiving

the 8 data bits, the X1227 again responds with an

acknowledge. The master then terminates the transfer

by generating a stop condition. The X1227 then begins

an internal write cycle of the data to the nonvolatile

memory. During the internal write cycle, the device

inputs are disabled, so the device will not respond to

any requests from the master. The SDA output is at high

impedance. See Figure 11.

Figure 11. Byte Write Sequence

Figure 12. Writing 30 bytes to a 64-byte memory page starting at address 40.

Slave

Address

Word

Address 1

Data

SDA Bus

Signals From

The Slave

Signals from

the Master

Word

Address 0

1111 0000000

Address

23 Bytes

7 Bytes

Address

= 6

Address Pointer

Ends Here

Addr = 7

Figure 10. Slave Address, Word Address, and Data Bytes (64 Byte pages)

Slave Address Byte

Byte 0

D7 D6 D5 D2D4 D3 D1 D0

A0A7 A2A4 A3 A1

Data Byte

Byte 3

A6 A5

00 000A80

11R/W

Device Identifier

Array

CCR

Word Address 1

Byte 1

Word Address 0

Byte 2

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A write to a protected block of memory is ignored, but

will still receive an acknowledge. At the end of the write

command, the X1227 will not initiate an internal write

cycle, and will continue to ACK commands.

Page Write

The X1227 has a page write operation. It is initiated in

the same manner as the byte write operation; but

instead of terminating the write cycle after the ﬁrst data

byte is transferred, the master can transmit up to 63

more bytes to the memory array and up to 7 more

bytes to the clock/control registers. (Note: Prior to writ-

ing to the CCR, the master must write a 02h, then 06h

to the status register in two preceding operations to

enable the write operation. See “Writing to the Clock/

Control Registers.”

After the receipt of each byte, the X1227 responds with

an acknowledge, and the address is internally incre-

mented by one. When the counter reaches the end of

the page, it “rolls over” and goes back to the ﬁrst

address on the same page. This means that the mas-

ter can write 64 bytes to a memory array page or 8

bytes to a CCR section starting at any location on that

page. For example, if the master begins writing at loca-

tion 40 of the memory and loads 30 bytes, then the ﬁrst

23 bytes are written to addresses 45 through 63, and

the last 7 bytes are written to columns 0 through 6.

Afterwards, the address counter would point to location

7 on the page that was just written. If the master sup-

plies more than the maximum bytes in a page, then the

previously loaded data is over written by the new data,

one byte at a time. Refer to Figure 12.

The master terminates the Data Byte loading by issu-

ing a stop condition, which causes the X1227 to begin

the nonvolatile write cycle. As with the byte write oper-

ation, all inputs are disabled until completion of the

internal write cycle. Refer to Figure 13 for the address,

acknowledge, and data transfer sequence.

Stops and Write Modes

Stop conditions that terminate write operations must

be sent by the master after sending at least 1 full data

byte and it’s associated ACK signal. If a stop is issued

in the middle of a data byte, or before 1 full data byte +

ACK is sent, then the X1227 resets itself without per-

forming the write. The contents of the array are not

affected.

Figure 13. Page Write Sequence

Word

Address 0

Slave

Address

Word

Address 1

Data

(n)

SDA Bus

Signals from

the Slave

Signals from

the Master

Data

(1)

1 ≤ n ≤ 64 for EEPROM array

1 ≤ n ≤ 8 for CCR

1111 0000000

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Acknowledge Polling

Disabling of the inputs during nonvolatile write cycles

can be used to take advantage of the typical 5mS write

cycle time. Once the stop condition is issued to indi-

cate the end of the master’s byte load operation, the

X1227 initiates the internal nonvolatile write cycle.

Acknowledge polling can begin immediately. To do this,

the master issues a start condition followed by the

Memory Array Slave Address Byte for a write or read

operation (AEh or AFh). If the X1227 is still busy with

the nonvolatile write cycle then no ACK will be

returned. When the X1227 has completed the write

operation, an ACK is returned and the host can pro-

ceed with the read or write operation. Refer to the ﬂow

chart in Figure 15. Note: Do not use the CCR slave

byte (DEh or DFh) for acknowledge polling.

Read Operations

There are three basic read operations: Current

Address Read, Random Read, and Sequential Read.

Current Address Read

Internally the X1227 contains an address counter that

maintains the address of the last word read incre-

mented by one. Therefore, if the last read was to

address n, the next read operation would access data

from address n+1. On power up, the sixteen bit

address is initialized to 0h. In this way, a current

address read immediately after the power on reset can

download the entire contents of memory starting at the

ﬁrst location.Upon receipt of the Slave Address Byte

with the R/W bit set to one, the X1227 issues an

acknowledge, then transmits eight data bits. The mas-

ter terminates the read operation by not responding

with an acknowledge during the ninth clock and issuing

a stop condition. Refer to Figure 14 for the address,

acknowledge, and data transfer sequence.

Figure 15. Acknowledge Polling Sequence

It should be noted that the ninth clock cycle of the read

operation is not a “don’t care.” To terminate a read

operation, the master must either issue a stop condi-

tion during the ninth cycle or hold SDA HIGH during

the ninth clock cycle and then issue a stop condition.

ACK

returned?

Issue Memory Array Slave

Address Byte AFh (Read)

or AEh (Write)

Byte load completed

by issuing STOP.

Enter ACK Polling

Issue STOP

Issue START

YES

Issue STOP

Continue normal

Read or Write

command

sequence

PROCEED

YES

nonvolatile write

Cycle complete. Continue

command sequence?

Figure 14. Current Address Read Sequence

Slave

Address

Data

SDA Bus

Signals from

the Slave

Signals from

the Master

11111

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Random Read

Random read operations allows the master to access

any location in the X1227. Prior to issuing the Slave

Address Byte with the R/W bit set to zero, the master

must ﬁrst perform a “dummy” write operation.

The master issues the start condition and the slave

address byte, receives an acknowledge, then issues

the word address bytes. After acknowledging receipt of

each word address byte, the master immediately

issues another start condition and the slave address

byte with the R/W bit set to one. This is followed by an

acknowledge from the device and then by the eight bit

data word. The master terminates the read operation

by not responding with an acknowledge and then issu-

ing a stop condition. Refer to Figure 16 for the address,

acknowledge, and data transfer sequence.

In a similar operation called “Set Current Address,” the

device sets the address if a stop is issued instead of

the second start shown in Figure 16. The X1227 then

goes into standby mode after the stop and all bus

activity will be ignored until a start is detected. This

operation loads the new address into the address

counter. The next Current Address Read operation will

read from the newly loaded address. This operation

could be useful if the master knows the next address it

needs to read, but is not ready for the data.

Sequential Read

Sequential reads can be initiated as either a current

address read or random address read. The ﬁrst data

byte is transmitted as with the other modes; however,

the master now responds with an acknowledge, indi-

cating it requires additional data. The device continues

to output data for each acknowledge received. The mas-

ter terminates the read operation by not responding with

an acknowledge and then issuing a stop condition.

The data output is sequential, with the data from

address n followed by the data from address n + 1. The

address counter for read operations increments

through all page and column addresses, allowing the

entire memory contents to be serially read during one

operation. At the end of the address space the counter

“rolls over” to the start of the address space and the

X1227 continues to output data for each acknowledge

received. Refer to Figure 17 for the acknowledge and

data transfer sequence.

Figure 16. Random Address Read Sequence

Slave

Address Word

Address 1

Slave

Address

Data

SDA Bus

Signals from

the Slave

Signals from

the Master

Word

Address 0

1111 1111

0000000

Figure 17. Sequential Read Sequence

Data

(2)

Slave

Address

Data

(n)

SDA Bus

Signals from

the Slave

Signals from

the Master

Data

(n-1)

(n is any integer greater than 1)

Data

(1)

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ABSOLUTE MAXIMUM RATINGS

Temperature Under Bias ................... -65°C to +135°C

Storage Temperature......................... -65°C to +150°C

Voltage on VCC, VBACK pin

(respect to ground)...............................-0.5V to 7.0V

Voltage on SCL, SDA, X1 and X2

pin (respect to ground) ............... -0.5V to 7.0V or 0.5V

above VCC or VBACK (whichever is higher)

DC Output Current .............................................. 5 mA

Lead Temperature (Soldering, 10 sec) ...............300°C

Stresses above those listed under “Absolute Maximum

Ratings” may cause permanent damage to the device.

This is a stress rating only and the functional operation

of the device at these or any other conditions above

those indicated in the operational sections of this

speciﬁcation is not implied. Exposure to absolute max-

imum rating conditions for extended periods may affect

device reliability.

DC OPERATING CHARACTERISTICS (Temperature = -40°C to +85°C, unless otherwise stated.)

OPERATING CHARACTERISTICS

Symbol Parameter Conditions Min Typ Max Unit Notes

VCC Main Power Supply 2.7 5.5 V

VBACK Backup Power Supply 1.8 5.5 V

VCB Switch to Backup Supply VBACK -0.2 VBACK -0.1 V

VBC Switch to Main Supply VBACK VBACK +0.2 V

Symbol Parameter Conditions Min Typ Max Unit Notes

ICC1 Read Active Supply

Current

VCC = 2.7V 400 µA 1, 5, 7, 14

VCC = 5.0V 800 µA

ICC2 Program Supply Current

(nonvolatile)

VCC = 2.7V 2.5 mA 2, 5, 7, 14

VCC = 5.0V 3.0 mA

ICC3 Main Timekeeping

Current

VCC = 2.7V 10 µA 3, 7, 8, 14, 15

VCC = 5.0V 20 µA

IBACK

Timekeeping Current –

(Low Voltage Sense

and Watchdog Timer

disabled

VBACK = 1.8V 1.25 µA 3, 6, 9, 14, 15

“See Perfor-

mance Data”

VBACK = 3.3V 1.5 µA

ILI Input Leakage Current 10 µA 10

ILO Output Leakage Current 10 µA 10

VIL Input LOW Voltage -0.5 VCC x 0.2 or

VBACK x 0.2 V13

VIH Input HIGH Voltage VCC x 0.7 or

VBACK x 0.7

VCC + 0.5 or

VBACK + 0.5 V13

VHYS Schmitt Trigger Input

Hysteresis VCC related level .05 x VCC or

.05 x VBACK V13

VOL1 Output LOW Voltage for

SDA and RESET

VCC = 2.7V 0.4 V11

VCC = 5.5V 0.4

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Notes: (1) The device enters the Active state after any start, and remains active: for 9 clock cycles if the Device Select Bits in the Slave

Address Byte are incorrect or until 200nS after a stop ending a read or write operation.

(2) The device enters the Program state 200nS after a stop ending a write operation and continues for tWC.

(3) The device goes into the Timekeeping state 200nS after any stop, except those that initiate a nonvolatile write cycle; tWC after a

stop that initiates a nonvolatile write cycle; or 9 clock cycles after any start that is not followed by the correct Device Select Bits in

the Slave Address Byte.

(4) For reference only and not tested.

(5) VIL = VCC x 0.1, VIH = VCC x 0.9, fSCL = 400KHz

(6) VCC = 0V

(7) VBACK = 0V

(8) VSDA = VSCL=VCC, Others = GND or VCC

(9) VSDA =VSCL=VBACK, Others = GND or VBACK

(10) VSDA = GND or VCC, VSCL = GND or VCC, VRESET = GND or VCC

(11) IOL = 3.0mA at 5.5V, 1.5mA at 2.7V

(12) IOH = -1.0mA at 5.5V, -0.4mA at 2.7V

(13) Threshold voltages based on the higher of Vcc or Vback.

(14) Using recommended crystal and oscillator network applied to X1 and X2 (25°C).

(15) Typical values are for TA = 25°C

Capacitance TA = 25°C, f = 1.0 MHz, VCC = 5V

Notes: (1) This parameter is not 100% tested.

(2) The input capacitance between x1 and x2 pins can be varied between 5pF and 19.75pF by using analog trimming registers

AC CHARACTERISTICS

AC Test Conditions

Figure 18. Standard Output Load for testing the device with VCC = 5.0V

Symbol Parameter Max. Units Test Conditions

COUT(1) Output Capacitance (SDA, RESET)10pFV

OUT = 0V

CIN(1) Input Capacitance (SCL) 10 pF VIN = 0V

Input Pulse Levels VCC x 0.1 to VCC x 0.9

Input Rise and Fall Times 10ns

Input and Output Timing

Levels VCC x 0.5

Output Load Standard Output Load

SDA

1533Ω

100pF

5.0V

For VOL= 0.4V

and IOL = 3 mA

Equivalent AC Output Load Circuit for VCC = 5V

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AC Specifications (TA = -40°C to +85°C, VCC = +2.7V to +5.5V, unless otherwise specified.)

Notes: (1) This parameter is not 100% tested.

(2) Cb = total capacitance of one bus line in pF.

TIMING DIAGRAMS

Bus Timing

Symbol Parameter Min. Max. Units

fSCL SCL Clock Frequency 400 kHz

tIN Pulse width Suppression Time at inputs 50(1) ns

tAA SCL LOW to SDA Data Out Valid 0.1 0.9 µs

tBUF Time the bus must be free before a new transmission can start 1.3 µs

tLOW Clock LOW Time 1.3 µs

tHIGH Clock HIGH Time 0.6 µs

tSU:STA Start Condition Setup Time 0.6 µs

tHD:STA Start Condition Hold Time 0.6 µs

tSU:DAT Data In Setup Time 100 ns

tHD:DAT Data In Hold Time 0 µs

tSU:STO Stop Condition Setup Time 0.6 µs

tDH Data Output Hold Time 50 ns

tRSDA and SCL Rise Time 20 +.1Cb(2) 300 ns

tFSDA and SCL Fall Time 20 +.1Cb(2) 300 ns

Cb Capacitive load for each bus line 400 pF

tSU:STO

tDH

tHIGH

tSU:STA tHD:STA

tHD:DAT

tSU:DAT

SCL

SDA IN

SDA OUT

tFtLOW

tBUF

tAA

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Write Cycle Timing

Power Up Timing

Notes: (1) Delays are measured from the time VCC is stable until the speciﬁed operation can be initiated. These parameters are not 100%

tested. VCC slew rate should be between 0.2mV/µsec and 50mV/µsec.

(2) Typical values are for TA = 25°C and VCC = 5.0V

Nonvolatile Write Cycle Timing

Note: (1) tWC is the time from a valid stop condition at the end of a write sequence to the end of the self-timed internal nonvolatile write cycle.

It is the minimum cycle time to be allowed for any nonvolatile write by the user, unless Acknowledge Polling is used.

WATCHDOG TIMER/LOW VOLTAGE RESET OPERATING CHARACTERISTICS

Watchdog/Low Voltage Reset Parameters (See Figures 3 and 4)

Symbol Parameter Min. Typ.(2) Max. Units

tPUR(1) Time from Power Up to Read 1 ms

tPUW(1) Time from Power Up to Write 5 ms

Symbol Parameter Min. Typ.(1) Max. Units

tWC(1) Write Cycle Time 5 10 ms

Symbols Parameters Min. Typ. Max. Unit

VPTRIP

Programmed Reset Trip Voltage

X1227-4.5A

X1227

X1227-2.7A

X1227-2.7

4.50

4.25

2.75

2.55

4.63

4.38

2.85

2.65

4.75

4.50

2.95

2.75

tRPD VCC Detect to RESET LOW 500 ns

tPURST Power Up Reset Time-out Delay 100 250 400 ms

tFVCC Fall Time 10 µs

tRVCC Rise Time 10 µs

tWDO

Watchdog Timer Period (Crystal=32.768kHz):

WD1=0, WD0=0

WD1=0, WD0=1

WD1=1, WD0=0

1.7

725

225

1.75

750

250

1.8

775

275

tRST Watchdog Reset Time-out Delay (Crystal=32.768kHz) 225 250 275 ms

tRSP 2-Wire interface 1 µs

VRVALID Reset Valid VCC 1.0 V

SCL

SDA

tWC

8th Bit of Last Byte ACK

Stop

Condition

Start

Condition

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VTRIP Programming Timing Diagram

VTRIP Programming Parameters

Parameter Description Min. Max. Units

tVPS VTRIP Program Enable Voltage Setup time 1 µs

tVPH VTRIP Program Enable Voltage Hold time 1 µs

tTSU VTRIP Setup time 1 µs

tTHD VTRIP Hold (stable) time 10 ms

tVPO

VTRIP Program Enable Voltage Off time

(Between successive adjustments) 0µs

tRP

VTRIP Program Recovery Period

(Between successive adjustments) 10 ms

VPProgramming Voltage 14 16 V

VTRAN VTRIP Programmed Voltage Range 1.7 5.0 V

Vtv

VTRIP Program variation after programming

(Programmed at 25°C) -25 +25 mV

VTRIP programming parameters are not 100% Tested.

01234567 01234567 01234567 01234567

VCC

(VTRIP)

tVPH

tVPS tVPO

tRP

SCL

SDA

AEh 03h/01h

RESET VP = 15V

00h00h

VCC

tTSU tTHD

VTRIP

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APPLICATION SECTION

CRYSTAL OSCILLATOR AND TEMPERATURE

COMPENSATION

Xicor has now integrated the oscillator compensation

circuity on-chip, to eliminate the need for external com-

ponents and adjust for crystal drift over temperature

and enable very high accuracy time keeping (<5ppm

drift.

The Xicor RTC family uses an oscillator circuit with on-

chip crystal compensation network, including adjust-

able load-capacitance. The only external component

required is the crystal. The compensation network is

optimized for operation with certain crystal parameters

which are common in many of the surface mount or

tuning-fork crystals available today. Table 6 summa-

rizes these parameters.

Table 7 contains some crystal manufacturers and part

numbers that meet the requirements for the Xicor RTC

products.

The turnover temperature in Table 6 describes the

temperature where the apex of the of the drift vs. tem-

perature curve occurs. This curve is parabolic with the

drift increasing as (T-T0)2. For an Epson MC-405

device, for example, the turnover temperature is typi-

cally 25 deg C, and a peak drift of >110ppm occurs at

the temperature extremes of –40 and +85 deg C. It is

possible to address this variable drift by adjusting the

load capacitance of the crystal, which will result in pre-

dictable change to the crystal frequency. The Xicor

RTC family allows this adjustment over temperature

since the devices include on-chip load capacitor trim-

ming. This control is handled by the Analog Trimming

capacitance range covered by the ATR circuit is

approximately 3.25pF to 18.75pF, in 0.25pf incre-

ments. Note that actual capacitance would also

include about 2pF of package related capacitance. In-

circuit tests with commercially available crystals dem-

onstrate that this range of capacitance allows fre-

quency control from +116ppm to –37ppm, using a

12.5pF load crystal.

In addition to the analog compensation afforded by the

adjustable load capacitance, a digital compensation

feature is available for the Xicor RTC family. There are

three bits known as the Digital Trimming Register or

DTR, and they operate by adding or skipping pulses in

the clock signal. The range provided is ±30ppm in

increments of 10ppm. The default setting is 0ppm. The

DTR control can be used for coarse adjustments of

frequency drift over temperature or for crystal initial

accuracy correction.

Table 6. Crystal Parameters Required for Xicor RTC’s

Table 7. Crystal Manufacturers

Parameter Min Typ Max Units Notes

Frequency 32.768 kHz

Freq. Tolerance ±100 ppm Down to 20ppm if desired

Turnover Temperature 20 25 30 °C Typically the value used for most

crystals

Operating Temperature Range -40 85 °C

Parallel Load Capacitance 12.5 pF

Equivalent Series Resistance 50 kΩFor best oscillator performance

Manufacturer Part Number Temp Range +25°C Freq Toler.

Citizen CM201, CM202, CM200S -40 to +85°C ±20ppm

Epson MC-405, MC-406 -40 to +85°C ±20ppm

Raltron RSM-200S-A or B -40 to +85°C ±20ppm

SaRonix 32S12A or B -40 to +85°C ±20ppm

Ecliptek ECPSM29T-32.768K -10 to +60°C ±20ppm

ECS ECX-306/ECX-306I -10 to +60°C ±20ppm

Fox FSM-327 -40 to +85°C ±20ppm

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A ﬁnal application for the ATR control is in-circuit cali-

bration for high accuracy applications, along with a

temperature sensor chip. Once the RTC circuit is pow-

ered up with battery backup, the frequency drift is mea-

sured. The ATR control is then adjusted to a setting

which minimizes drift. Once adjusted at a particular

temperature, it is possible to adjust at other discrete

temperatures for minimal overall drift, and store the

resulting settings in the EEPROM. Extremely low over-

all temperature drift is possible with this method. The

Xicor evaluation board contains the circuitry necessary

to implement this control.

For more detailed operation see Xicor’s application

note AN154 on Xicor’s website at www.xicor.com.

Layout Considerations

The crystal input at X1 has a very high impedance and

will pick up high frequency signals from other circuits

on the board. Since the X2 pin is tied to the other side

of the crystal, it is also a sensitive node. These signals

can couple into the oscillator circuit and produce dou-

ble clocking or mis-clocking, seriously affecting the

accuracy of the RTC. Care needs to be taken in layout

of the RTC circuit to avoid noise pickup. Below in Fig-

ure 15 is a suggested layout for the X1226 or X1227

devices.

Figure 15. Suggested Layout for Xicor RTC in SO-8

The X1 and X2 connections to the crystal are to be

kept as short as possible. A thick ground trace around

the crystal is advised to minimize noise intrusion, but

ground near the X1 and X2 pins should be avoided as

it will add to the load capacitance at those pins. Keep in

mind these guidelines for other PCB layers in the vicin-

ity of the RTC device. A small decoupling capacitor at

the Vcc pin of the chip is mandatory, with a solid con-

nection to ground.

For other RTC products, the same rules stated above

should be observed, but adjusted slightly since the

packages and pinouts are slightly different.

Assembly

Most electronic circuits do not have to deal with

assembly issues, but with the RTC devices assembly

includes insertion or soldering of a live battery into an

unpowered circuit. If a socket is soldered to the board,

and a battery is inserted in ﬁnal assembly, then there

are no issues with operation of the RTC. If the battery

is soldered to the board directly, then the RTC device

Vback pin will see some transient upset from either sol-

dering tools or intermittent battery connections which

can stop the circuit from oscillating. Once the battery is

soldered to the board, the only way to assure the circuit

will start up is to momentarily (very short period of

time!) short the Vback pin to ground and the circuit will

begin to oscillate.

Oscillator Measurements

When a proper crystal is selected and the layout guide-

lines above are observed, the oscillator should start up

in most circuits in less than one second. Some circuits

may take slightly longer, but startup should deﬁnitely

occur in less than 5 seconds. When testing RTC cir-

cuits, the most common impulse is to apply a scope

probe to the circuit at the X2 pin (oscillator output) and

observe the waveform. DO NOT DO THIS! Although in

some cases you may see a useable waveform, due to

the parasitics (usually 10pF to ground) applied with the

scope probe, there will be no useful information in that

waveform other than the fact that the circuit is oscillat-

ing. The X2 output is sensitive to capacitive impedance

so the voltage levels and the frequency will be affected

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by the parasitic elements in the scope probe. Applying

a scope probe can possibly cause a faulty oscillator to

start up, hiding other issues (although in the Xicor

RTC’s, the internal circuitry assures startup when

using the proper crystal and layout). The best way to

analyze the RTC circuit is to power it up and read the

real time clock as time advances.

Backup Battery Operation

Many types of batteries can be used with the Xicor

RTC products. 3.0V or 3.6V Lithium batteries are

appropriate, and sizes are available that can power a

Xicor RTC device for up to 10 years. Another option is

to use a supercapacitor for applications where Vcc may

disappear intermittently for short periods of time.

Depending on the value of supercapacitor used,

backup time can last from a few days to two weeks

(with >1F). A simple silicon or Schottky barrier diode

can be used in series with Vcc to charge the superca-

pacitor, which is connected to the Vback pin. Do not

use the diode to charge a battery (especially lithium

batteries!).

Figure 16. Supercapacitor charging circuit

Since the battery switchover occurs at Vcc=Vback-

0.1V (see Figure 16), the battery voltage must always

be lower than the Vcc voltage during normal operation

or the battery will be drained. A second consideration

is the trip point setting for the system RESET- function,

known as Vtrip. Vtrip is set at the factory at levels for

systems with either Vcc = 5V or 3.3V operation, with

the following standard options:

VTRIP = 4.63V ± 3%

VTRIP = 4.38V ± 3%

VTRIP = 2.85V ± 3%

VTRIP = 2.65V ± 3%

The summary of conditions for backup battery opera-

tion is given in Table 8:

2.7-5.5V

Supercapacitor

back

Table 8. Battery Backup Operation

*since Vback>2.65V is higher than Vtrip, the battery is powering the entire device

1. Example Application, Vcc=5V, Vback=3.0V

Condition Vcc Vback Vtrip Iback Reset Notes

a. Normal Operation 5.00 3.00 4.38 <<1µA H

b. Vcc on with no battery 5.00 0 4.38 0 H

c. Backup Mode 0–1.8 1.8-3.0 4.38 <2µA L Timekeeping

only

2. Example Application, Vcc=3.3V,Vback=3.0V

Condition Vcc Vback Vtrip Iback Reset

a. Normal Operation 3.30 3.00 2.65 <<1µA H

b. Vcc on with no battery 3.30 0 2.65 0 H

c. Backup Mode 0–1.8 1.8–3.0* 2.65 <2µA* L Timekeeping

only

d. UNWANTED - Vcc ON, Vback

powering 2.65 - 3.30 > Vcc 2.65 up to 3mA H Internal

Vcc=Vback

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Referring to Figure 16, Vtrip applies to the “Internal

Vcc” node which powers the entire device. This means

that if Vcc is powered down and the battery voltage at

Vback is higher than the Vtrip voltage, then the entire

chip will be running from the battery. If Vback falls to

lower than Vtrip, then the chip shuts down and all out-

puts are disabled except for the oscillator and time-

keeping circuitry. The fact that the chip can be powered

from Vback is not necessarily an issue since standby

current for the RTC devices is <2µA for this mode

(called “main timekeeping current” in the data sheet).

Only when the serial interface is active is there an

increase in supply current, and with Vcc powered

down, the serial interface will most likely be inactive.

One way to prevent operation in battery backup mode

above the Vtrip level is to add a diode drop (silicon

diode preferred) to the battery to insure it is below

Vtrip. This will also provide reverse leakage protection

which may be needed to get safety agency approval.

One mode that should always be avoided is the opera-

tion of the RTC device with Vback greater than both

Vcc and Vtrip (Condition 2d in Table 8). This will cause

the battery to drain quickly as serial bus communica-

tion and non-volatile writes will require higher supplier

current.

PERFORMANCE DATA

IBACK Performance

1.4

1.2

1.0

0.8

0.6

0.4

0.2

IBACK vs. Temperature

Multi-Lot Process Variation Data

Temperature °C

-40 25 60 85

IBACK (µA)

3.3V

1.8V

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PACKAGING INFORMATION

0.150 (3.80)

0.158 (4.00)

0.228 (5.80)

0.244 (6.20)

0.014 (0.35)

0.019 (0.49)

Pin 1

Pin 1 Index

0.010 (0.25)

0.020 (0.50)

0.050 (1.27)

0.188 (4.78)

0.197 (5.00)

0.004 (0.19)

0.010 (0.25)

0.053 (1.35)

0.069 (1.75)

(4X) 7°

0.016 (0.410)

0.037 (0.937)

0.0075 (0.19)

0.010 (0.25)

0° - 8°

X 45°

8-Lead Plastic, SOIC, Package Code S8

NOTE: ALL DIMENSIONS IN INCHES (IN PARENTHESES IN MILLIMETERS)

0.250"

0.050"Typical

0.050"

Typical

0.030"

Typical

8 PlacesFOOTPRINT

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PACKAGING INFORMATION

NOTE: ALL DIMENSIONS IN INCHES (IN PARENTHESES IN MILLIMETERS)

8-Lead Plastic, TSSOP, Package Code V8

See Detail “A”

.031 (.80)

.041 (1.05)

.169 (4.3)

.177 (4.5) .252 (6.4) BSC

.025 (.65) BSC

.114 (2.9)

.122 (3.1)

.002 (.05)

.006 (.15)

.047 (1.20)

.0075 (.19)

.0118 (.30)

0° – 8°

.010 (.25)

.019 (.50)

.029 (.75)

Gage Plane

Seating Plane

Detail A (20X)

(4.16) (7.72)

(1.78)

(0.42)

(0.65)

All Measurements Are Typical

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ORDERING INFORMATION

Note: For appropriate volume, any VTRIP value from 2.6 to 4.7V may be ordered via Xicor’s Customer Speciﬁcation Program (CSPEC).

VCC Range VTRIP Package Operating Temperature Range Part Number

2.7 – 5.5V 4.63V ± 112mV 8L SOIC 0–70°C X1227S8-4.5A

-40–85°C X1227S8I-4.5A

2.7 – 5.5V 4.63V ± 112mV 8L TSSOP 0–70°C X1227V8-4.5A

-40–85°C X1227V8I-4.5A

2.7 – 5.5V 4.38V ± 112mV 8L SOIC 0–70°C X1227S8

-40–85°C X1227S8I

2.7 – 5.5V 4.38V ± 112mV 8L TSSOP 0–70°C X1227V8

-40–85°C X1227V8I

2.7 – 5.5V 2.85V ± 100mV 8L SOIC 0–70°C X1227S8-2.7A

-40–85°C X1227S8I-2.7A

2.7 – 5.5V 2.85V ± 100mV 8L TSSOP 0–70°C X1227V8-2.7A

-40–85°C X1227V8I-2.7A

2.7 – 5.5V 2.65V ± 100mV 8L SOIC 0–70°C X1227S8-2.7

-40–85°C X1227S8I-2.7

2.7 – 5.5V 2.65V ± 100mV 8L TSSOP 0–70°C X1227V8-2.7

-40–85°C X1227V8I-2.7

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LIMITED WARRANTY

Devices sold by Xicor, Inc. are covered by the warranty and patent indemniﬁcation provisions appearing in its Terms of Sale only. Xicor, Inc. makes no warranty,

express, statutory, implied, or by description regarding the information set forth herein or regarding the freedom of the described devices from patent infringement.

Xicor, Inc. makes no warranty of merchantability or ﬁtness for any purpose. Xicor, Inc. reserves the right to discontinue production and change speciﬁcations and prices

at any time and without notice.

Xicor, Inc. assumes no responsibility for the use of any circuitry other than circuitry embodied in a Xicor, Inc. product. No other circuits, patents, or licenses are implied.

COPYRIGHTS AND TRADEMARKS

Xicor, Inc., the Xicor logo, E2POT, XDCP, XBGA, AUTOSTORE, Direct Write cell, Concurrent Read-Write, PASS, MPS, PushPOT, Block Lock, IdentiPROM,

E2KEY, X24C16, SecureFlash, and SerialFlash are all trademarks or registered trademarks of Xicor, Inc. All other brand and product names mentioned herein are

used for identification purposes only, and are trademarks or registered trademarks of their respective holders.

U.S. PATENTS

Xicor products are covered by one or more of the following U.S. Patents: 4,326,134; 4,393,481; 4,404,475; 4,450,402; 4,486,769; 4,488,060; 4,520,461; 4,533,846;

4,599,706; 4,617,652; 4,668,932; 4,752,912; 4,829,482; 4,874,967; 4,883,976; 4,980,859; 5,012,132; 5,003,197; 5,023,694; 5,084,667; 5,153,880; 5,153,691;

5,161,137; 5,219,774; 5,270,927; 5,324,676; 5,434,396; 5,544,103; 5,587,573; 5,835,409; 5,977,585. Foreign patents and additional patents pending.

LIFE RELATED POLICY

In situations where semiconductor component failure may endanger life, system designers using this product should design the system with appropriate error detection

and correction, redundancy and back-up features to prevent such an occurrence.

Xicor’s products are not authorized for use in critical components in life support devices or systems.

1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to

perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a signiﬁcant injury to the user.

2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life

support device or system, or to affect its safety or effectiveness.

PART MARK INFORMATION

8-Lead TSSOP

YWW

XXXXX

1227AL = 4.5 to 5.5V, 0 to +70°C, V

TRIP

= 4.63V ± 112mV

1227AM = 4.5 to 5.5V, -40 to +85°C, V

TRIP

= 4.63V ± 112mV

1227 = 4.5 to 5.5V, 0 to +70°C, V

TRIP

= 4.38V ± 112mV

1227I = 4.5 to 5.5V, -40 to +85°C, V

TRIP

= 4.38V ± 112mV

1227AN = 2.7 to 5.5V, 0 to +70°C, V

TRIP

= 2.85V ± 100mV

1227AP = 2.7 to 5.5V, -40 to +85°C, V

TRIP

= 2.85V ± 100mV

1227F = 2.7 to 5.5V, 0 to +70°C, V

TRIP

= 2.65V ± 100mV

1227G = 2.7 to 5.5V, -40 to +85°C, V

TRIP

= 2.65V ± 100mV

8-Lead SOIC

X1227 X

Blank = 8-Lead SOIC

AL = 4.5 to 5.5V, 0 to +70°C, V

TRIP

= 4.63V ± 112mV

AM = 4.5 to 5.5V, -40 to +85°C, V

TRIP

= 4.63V ± 112mV

Blank = 4.5 to 5.5V, 0 to +70°C, V

TRIP

= 4.38V ± 112mV

I = 4.5 to 5.5V, -40 to +85°C, V

TRIP

= 4.38V ± 112mV

AN = 2.7 to 5.5V, 0 to +70°C, V

TRIP

= 2.85V ± 100mV

AP = 2.7 to 5.5V, -40 to +85°C, V

TRIP

= 2.85V ± 100mV

F = 2.7 to 5.5V, 0 to +70°C, V

TRIP

= 2.65V ± 100mV

G = 2.7 to 5.5V, -40 to +85°C, V

TRIP

= 2.65V ± 100mV