X1288 Datasheet, PDF (9/27 Pages) Xicor Inc. – 2-Wire RTC Real Time Clock/Calendar/CPU Supervisor with EEPROM

X1288
The device offers a backup power input pin. This V_BACK
pin allows the device to be backed up by battery or
SuperCap. The entire X1288 device is fully operational
from 2.7 to 5.5 volts and the clock/calendar portion of the
X1288 device remains fully operational down to 1.8 volts
(Standby Mode).
The X1288 device provides 256K 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
NC
NC
NC
NC
RESET
V_SS
16 Ld SOIC
1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
X1288
14 Ld TSSOP
V_CC
X1 ₁
V_BACK
X2 2
PHZ/IRQ _{NC 3}
NC
NC ₄
NC
NC 5
NC
RESET 6
SCL
SDA
V_{SS 7}
14
V_CC
13
V_BACK
12 ^PHZ/IRQ
11 ^NC
10 ^NC
9 ^SCL
8 SDA
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 out-
puts. The input buffer is always active (not gated).
An open drain output requires the use of a pull-up resis-
tor. 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 interface speed.
V_BACK
This input provides a backup supply voltage to the
device. V_BACK supplies power to the device in the event
the V_CC supply fails. This pin can be connected to a bat-
tery, 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 5kΩ. If unused, tie
to ground.
Programmable Frequency/Interrupt Output – PHZ/IRQ
This is either an output from the internal oscillator or an
interrupt signal output. It is a CMOS output.
9
When used as frequency output, this signal has a fre-
quency of 32.768kHz, 100Hz, 1Hz or inactive.
When used as interrupt output, this signal notifies a host
processor that an alarm has occurred and an action is
required. It is an active LOW output.
The control bits for this function are FO1 and FO0 and
are found in address 0011h of the Clock Control Memory
map. See “Programmable Frequency Output Bits - FO1,
FO0” on page 13.
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 X1288 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 information.
X1
X2
FIGURE 2. RECOMMENDED CRYSTAL CONNECTION
POWER CONTROL OPERATION
The power control circuit accepts a V_CC and a V_BACK
input. The power control circuit powers the clock from
V_BACK when V_CC < V_BACK - 0.2V. It will switch back to
power the device from V_CC when V_CC exceeds V_BACK.
V_BACK
V_CC
Off
Voltage
On
In
FIGURE 3. POWER CONTROL
REAL TIME CLOCK OPERATION
The Real Time Clock (RTC) uses an external 32.768kHz
quartz crystal to maintain an accurate internal represen-
tation of the 1/100 of a second, second, minute, hour,
day, date, month, and year. The RTC has leap-year cor-
rection. 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 X1288 powers up after the loss
of both V_CC and V_BACK, the clock will not operate until at
least one byte is written to the clock register.
FN8102.3
April 14, 2006