ISL1209_06 Datasheet, PDF (20/24 Pages) Intersil Corporation – Low Power RTC with Battery Backed SRAM and Event Detection

ISL1209
Application Section
Event Detection
The event detection feature of the ISL1209 is intended to be
used for recording the time of single events that involve the
opening of an enclosure, door, etc. The normal method of
detection is with normally closed switch function that opens
to initiate the event. This mechanism is ideal for applications
such as set top boxes, utility meters, security alarm and
camera systems or vending machines.
A typical application diagram is shown in Figure 17. A
microcontroller communicates with the ISL1209 through the
I²C serial bus, to set up and read time of the day, alarms, or
set up the outputs frequency control.
A general purpose I/O pin can be used to monitor the
ISL1209’s EVDET-pin and take action. Options include
waking up the microcontroller to proceed with an activity, or
simply logging the time of the event in memory.
An additional event action available in the ISL1209 is to stop
the real time clock from advancing. If the event register is set
to enable this function (Register 09h, RTCHLT bit 5 set to 1),
then when the EVIN pin is triggered, the clock counters will
stop and hold the time of the event. This is useful for one
time occurrences such as opening a warranted consumer
product enclosure or exceeding a maximum temperature
inside a device. Once the clock is stopped, the clock
registers must be written with an updated time, then they will
begin advancing immediately. If the RTCHLT bit is still set,
then the next event will again stop the clock.
Event Detect Input Details
The EVIN input is a Schmitt trigger logic input. An event is
detected when it is asserted high. The ISL1209 device has
internal configuration settings which add detection flexibility.
There are four configuration bits in register 09h which are for
EVIN sampling. The ESMP1 and ESMP0 bits control
sampling of the event input status. Reducing the sampling
rate will lower the supply current drain, with the tradeoff of
adding a delay in detecting an event. An event that is long in
duration (i.e. opening a door) would obviously be served well
with the lowest frequency sampling rate and lowest supply
current drain.
The EHYS1 and EHYS0 bits control timer circuits to filter out
switch bouncing, noise or intermittent contacts, by effectively
adding time-based hysteresis to the EVIN input. They are
used only in conjunction with the sampling rate, they cannot
be used alone. The most appropriate use for the hysteresis
function is for glitch or noise filtering on the EVIN input
signal.
Battery Backup Details
The event detection function has been designed to minimize
power drain for extended life in battery backed applications.
Many applications will need detection while in battery
backup. Another bit, the EVBATB bit, is used to control if the
event input is active in battery backup mode. Note that to
DISABLE event sampling in battery backup, this bit is set to
1. The occurrence of an event is recorded and can be read
by the microprocessor the next time the circuit is powered
up. The input current sources and sampling are also usable
in battery backup mode. If the EVIENB bit is set to disable
the input current source, a large value pullup resistor must
V_CC
5.1k
Micro C.
P0
P1
P2
P3
P4
P5
SCL
SDA
1M**
32.768kHz
ISL1209
2M*
1
X1
10
Vcc
2 _X2
IRQ/F ⁹
5.1k
3 V_BAT
SCL ⁸
4 _VDD
5 _EVIN
SDA ⁷
EVDET ⁶
3.0V
Event Detect Switch Normally Closed
* Optional Pull Up resistors, or use internal current
Source
** The Pull up resistor on the EVDET-output can vary
from 10k up to 10M or more, depending on the
application
FIGURE 17.
20
FN6109.4
October 17, 2006