X1227
DESCRIPTION (continued)
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).
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.
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).
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.
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.
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
V
BACK
specified threshold. The V
threshold is user repro-
This input provides a backup supply voltage to the
trip
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.
device. V
event the V
supplies power to the device in the
supply fails. This pin can be connected
BACK
CC
to a battery, a Supercap or tied to ground if not used.
RESET Output – RESET
The device offers a backup power input pin. This
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
old. It is an open drain active LOW output. Recom-
mended value for the pullup resistor is 5K Ohms. If
unused, tie to ground.
V
pin allows the device to be backed up by battery
BACK
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).
thresh-
TRIP
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.
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.
PIN DESCRIPTIONS
X1227
8-Pin SOIC
1
2
V
V
X1
X2
8
7
6
5
CC
BACK
RESET
3
4
SCL
SDA
V
SS
Figure 1. Recommended Crystal connection
X1227
8-Pin TSSOP
V
SCL
SDA
BACK
1
2
3
4
8
7
6
5
X1
X2
V
CC
X1
X2
V
SS
RESET
NC = No internal connection
REV 1.1.20 1/13/03
Characteristics subject to change without notice. 2 of 28
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