X1205V8I
| Model | X1205V8I |
| Description | Real Time Clock/Calendar |
| PDF file | Total 22 pages (File size: 408K) |
| Chip Manufacturer | XICOR |
X1205 – Preliminary Information
DESCRIPTION
(continued)
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 or provide
a hardware interrupt (IRQ Pin). There is a repeat
mode for the alarms allowing a periodic interrupt.
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 X1205 device is fully
operational from 2.7 to 5.5 volts and the clock/calendar
portion of the X1205 device remains fully operational
down to 1.8 volts (Standby Mode).
PIN DESCRIPTIONS
X1205
8-Pin SOIC
X1
X2
IRQ
V
SS
1
2
3
4
8
7
6
5
V
CC
V
BACK
SCL
SDA
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 X1205 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.
R
Off
Figure 1. Recommended Crystal connection
X1
X2
8-Pin TSSOP
V
BACK
V
CC
X1
X2
1
2
3
4
8
7
6
5
SCL
SDA
V
SS
IRQ
NC = No internal connection
M
EL
I
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).
IN
A
V
BACK
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
.
Figure 2. Power Control
V
CC
Voltage
On
In
PR
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. This pin can be connected
to a battery, a Supercap or tied to ground if not used.
Interrupt Output – IRQ
This is an interrupt signal output. This signal notifies a
host processor that an alarm has occurred and
requests action. It is an open drain active low output.
REV 1.0.9 8/29/02
REAL TIME CLOCK OPERATION
The Real Time Clock (RTC) uses an external
32.768kHz quartz crystal to maintain an accurate inter-
nal representation of 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 X1205 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.
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
Characteristics subject to change without notice.
Y
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