X1243 Datasheet, PDF (2/17 Pages) Xicor Inc. – Real Time Clock/Calendar/Alarm with EEPROM

X1243
Pin Configuration
X1243
8-Pin SOIC
X1 1
X2 ²
IRQ 3
V_SS
4
8
V_CC
7
V_Back
6 SCL
5 SDA
X1243
8-Pin TSSOP
V_{Back 1}
V_{CC 2}
X1 3
X2 4
8 ^SCL
7 ^SDA
6 ^VSS
5 IRQ
12pF
10M
X1
X2
68pF
360K
FIGURE 1. RECOMMENDED CRYSTAL CONNECTION
Power Control Operation
The Power control circuit accepts a V_CC and a V_BACK input.
The power control circuit will switch to V_BACK when V_CC <
V_BACK – 0.2V. It will switch back to V_CC when V_CC exceeds
V_BACK.
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.
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.
Interrupt Output—IRQ
This is an interrupt signal output. This signal noties a host
processor that alarm has occurred and requests action. It is
an open drain active LOW output.
X1, X2
The X1 and X2 pins are the input and output, respectively, of
an inverting amplier that can be con-gured for use as an on-
chip oscillator. A 32.768kHz quartz crystal is used.
Recommended crystal is a Citizen CFS-206. The crystal
supplies a timebase for a clock/ oscillator. The internal clock
can be driven by an external signal on X1, with X2 left
unconnected.
V_BACK
V_CC = V_BACK -0.2V
V_CC
Internal
Voltage
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 repre-
sentation of the year, month, day, date, hour, minute, and
seconds. The RTC has leap-year correction and a century
byte. The clock will also correct for months hav-ing fewer
than 31 days and will have a bit that controls 24-hour or
AM/PM format. When the X1243 powers up after the loss of
both V_CC and V_BACK, the clock will not increment 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 nite amount of time, there is the
possibility that the clock could change dur-ing 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.
2
FN8249.0
April 28, 2005