Rainbow Electronics DS1687 - Manual (Page 5)

DS1685/DS1687
5 of 38
set. To clear the IRQ pin, the application software must clear all enabled flag bits contributing to IRQ ’s
active state.
When no interrupt conditions are present, the IRQ level is in the high-impedance state. Multiple
interrupting devices can be connected to an IRQ bus. The IRQ pin is an open-drain output and requires an
external pullup resistor. The voltage on the pullup supply should be no greater than V
CC
+ 0.2V.
PWR (Power-On Output; Open Drain, Active Low) – The PWR pin is intended for use as an on/off
control for the system power. With V
CC
voltage removed from the DS1685/DS1687, PWR can be
automatically activated from a kickstart input by the KS pin or from a wake-up interrupt. Once the
system is powered on, the state of PWR can be controlled by bits in the Dallas registers. The PWR pin
can be connected through a pullup resistor to a positive supply. For 5V operation, the voltage of the
pullup supply should be no greater than 5.7V. For 3V operation, the voltage of the pullup supply should
be no greater than 3.9V.
KS (Kickstart Input; Active Low) – When V
CC
is removed from the DS1685/DS1687, the system can
be powered on in response to an active-low transition on the KS pin, as might be generated from a key
closure. V
BAUX
must be present and the auxiliary-battery enable bit (ABE) must be set to 1 if the kickstart
function is used, and the KS pin must be pulled up to the V
BAUX
supply. While V
CC
is applied, the KS pin
can be used as an interrupt input.
RCLR (RAM Clear Input; Active Low) – If enabled by software, taking RCLR low clears the 242
bytes of user RAM. When enabled, RCLR can be activated whether or not V
CC
is present. The RCLR
function is designed to be used by a human interface (shorting to ground manually or by a switch) and not
to be driven with external buffers. This pin is internally pulled up. Do not use an external pullup resistor
on this pin.
V
BAUX
– Auxiliary battery input required for kickstart and wake-up features. This input also supports
clock/ calendar and user RAM if V
BAT
is at lower voltage or is not present. A standard +3V lithium cell or
other energy source can be used. Battery voltage must be held between +2.5V and +3.7V for proper
operation. If V
BAUX
is not going to be used it should be grounded, and auxiliary-battery enable bit bank 1,
register 4BH, should equal 0.
See “Conditions of Acceptability” at http://www.maxim-ic.com/TechSupport/QA/ntrl.htm .
DS1685 ONLY
X1, X2 – Connections for a standard 32.768kHz quartz crystal. For greatest accuracy, the DS1685 must
be used with a crystal that has a specified load capacitance of either 6pF or 12.5pF. The crystal-select
(CS) bit in Extended Control Register 4B is used to select operation with a 6pF or 12.5pF crystal. The
crystal is attached directly to the X1 and X2 pins. There is no need for external capacitors or resistors.
Note: X1 and X2 are very high-impedance nodes. It is recommended that they and the crystal be guard-
ringed with ground and that high-frequency signals be kept away from the crystal area.