DS1689SSLASHR datasheet(20/36 Pages) DALLAS

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DS1689/DS1693

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applied, the on-chip logic always attempts to drive the

PWR pin active in response to the enabled

kickstart or wake-up condition. This is true even if

PWR was previously inactive as the result of power

being applied by some means other than wake-up or kickstart.

The system can be powered down under software control by setting the PAB bit to logic 1. This causes

the open-drain

PWR pin to be placed in a high-impedance state, as shown at the beginning of interval 4 in

the timing diagram. As VCC voltage decays, the IRQ output pin is placed in a high-impedance state when

VCC goes below VPF. If the system is to be again powered on in response to a wake-up or kickstart, then

both the WF and KF flags should be cleared and WIE and/or KSE should be enabled prior to setting the

PAB bit.

During interval 5, the system is fully powered down. Battery backup of the clock calendar and NV RAM

is in effect,

PWR and IRQ are tri-stated, and monitoring of wake-up and kickstart takes place.

RAM CLEAR

The DS1689/DS1693 provide a RAM clear function for the 114 bytes of user RAM. When enabled, this

function can be performed regardless of the condition of the VCC pin.

The RAM clear function is enabled or disabled via the RAM Clear Enable bit (RCE; bank 1, register

04BH). When this bit is set to logic 1, the 114 bytes of user RAM are cleared (all bits set to 1) when an

active-low transition is sensed on the

RCLR pin. This action has no effect on either the clock/calendar

settings or upon the contents of the external extended RAM. The RAM clear flag (RF, bank 1, register

04BH) is set when the RAM clear operation has been completed. If VCC is present at the time of the RAM

clear and RIE = 1, the

IRQ line is also driven low upon completion. The interrupt condition can be

cleared by writing a 0 to the RF bit. The

IRQ line then returns to its inactive high level, provided there are

no other pending interrupts. Once the

RCLR pin is activated, all read/write accesses are locked out for a

minimum recover time, specified as tREC in the Electrical Characteristics section.

When RCE is cleared to 0, the RAM clear function is disabled. The state of the

RCLR pin has no effect

on the contents of the user RAM, and transitions on the

RCLR pin have no effect on RF.

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