DS1689SSLASHT&R datasheet(7/36 Pages) MAXIM

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DS1689/DS1693

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POWER-DOWN/POWER-UP CONSIDERATIONS

The real-time clock function will continue to operate and all of the RAM, time, calendar, and alarm

memory locations remain nonvolatile regardless of the level of the VCCI input. When VCCI is applied to

the DS1689/DS1693 and reaches a level of greater than VPF (power fail trip point), the device becomes

accessible after tREC, provided that the oscillator is running and the oscillator countdown chain is not in

reset (see Register A). This time period allows the system to stabilize after power is applied.

When PSEL is floating or logic 0, the DS1689 is in autosense mode and 3V or 5V operation is

determined based on the voltage on VCCI. Selection of 5V operation is automatically invoked when VCCI

rises above 4.5V for a minimum of tREC. However, 3V operation is automatically selected if VCCI does not

rise above the level of 4.25V. Selection of the power supply input levels requires 150ms of input stability

before operation can commence.

When 5V operation is selected, the device is fully accessible and data can be written and read only when

VCCI is greater than 4.5V. When VCCI is below 4.5V, read and writes are inhibited. However, the

timekeeping function continues unaffected by the lower input voltage. As VCC falls below the greater of

VBAT and VBAUX, the RAM and timekeeper are switched over to a lithium battery connected either to the

VBAT pin or VBAUX pin.

When 3V operation is selected and applied within normal limits, the device is fully accessible and data

can be written or read. When VCCI falls below VPF, access to the device is inhibited. If VPF is less than

VBAT and VBAUX, the power supply is switched from VCCI to the backup supply (the greater of VBAT and

VBAUX) when VCCI drops below VPF. If VPF is greater than VBAT and VBAUX, the power supply is switched

from VCCI to the backup supply when VCCI drops below the larger of VBAT and VBAUX.

When VCC falls below VPF, the chip is write-protected. With the possible exception of the KS, PWR, and

SQW pins, all inputs are ignored and all outputs are in a high impedance state.

RTC ADDRESS MAP

The address map for the RTC registers of the DS1689/DS1693 is shown in Figure 2. The address map

consists of the 14-clock/calendar registers. Ten registers contain the time, calendar, and alarm data, and

four bytes are used for control and status. All registers can be directly written or read except for the

following:

1. Registers C and D are read-only.

2. Bit 7 of Register A is read-only.

3. The high order bit of the seconds byte is read-only.

DS1689S/T&R датащи(PDF) 7 Page - Maxim Integrated Products