DS1685 Datasheet, PDF(5/33 Page) Maxim Integrated Products

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DS1685 Datasheet, PDF (5/33 Pages) Maxim Integrated Products – 3V/5V Real-Time Clocks

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DS1685/DS1687 3V/5V Real-Time Clocks

PIN DESCRIPTIONS (continued)

DS1685

DIP, SO,

TSSOP

PLCC

DS1687

EDIP

NAME

FUNCTION

IRQ

VBAT

RCLR

VBAUX

SQW

VCC

Kickstart Input, Active Low. When VCC 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.

VBAUX must be present and the auxiliary-battery enable bit (ABE) and kick-

start enable bit (KSE) must be set to 1 if the kickstart function is used, and

the KS pin must be pulled up to the VBAUX supply. While VCC is applied, the

KS pin can be used as an interrupt input. If not used, connect to VCC, or to

VBAUX if VBAUX is used.

Interrupt-Request Output, Open Drain, Active Low. The IRQ pin is an

active-low output of the DS1685/DS1687 that can be connected to the

interrupt input of a processor. The IRQ output remains low as long as the

status bit causing the interrupt is present and the corresponding interrupt-

enable bit is set. To clear the IRQ pin, the application software must clear

all the enabled flag bits contributing to IRQâs active state asserted but

without asserting CS latch addresses. However, no data transfer occurs.

Battery input for any standard 3V lithium cell or other energy source.

Battery voltage must be held between 2.5V and 3.7V for proper operation.

VBAT must be grounded if not used. Diodes should not be placed between

VBAT and the battery. See âConditions of Acceptabilityâ at

www.maxim-ic.com/UL.

RAM Clear Input, Active Low. If enabled by software, taking RCLR low

clears the 242 bytes of user RAM to FFh. When enabled, RCLR can be

activated whether or not VCC 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.

Auxiliary Battery Input. Required for kickstart and wake-up features. This

input also supports clock/ calendar and user RAM if VBAT 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 VBAUX is not going to be used it should be grounded, and

Auxiliary-Battery Enable bit bank 1, register 4BH, should be written to 0.

See âConditions of Acceptabilityâ at www.maxim-ic.com/UL.

Square-Wave Output. The SQW pin provides a 32kHz square-wave output,

tREC, after a power-up condition has been detected. This condition sets the

following bits, enabling the 32kHz output; DV1 = 1, and E32K = 1. A square

wave is output on this pin if either SQWE = 1 or E32K = 1. If E32K = 1, then

32kHz is output regardless of the other control bits. If E32K = 0, then the

output frequency is dependent on the control bits in register A. The SQW

pin can output a signal from one of 13 taps provided by the 15 internal

divider stages of the RTC. The frequency of the SQW pin can be changed

by programming Register A as shown in Table 3. The SQW signal can be

turned on and off using the SQWE bit in register B or the E32K bit in

extended register 4Bh. A 32kHz SQW signal is output when the enable-

32kHz (E32K) bit in extended register 4Bh is a logic 1 and VCC is above

VPF. A 32kHz square wave is also available when VCC is less than VPF if

E32K = 1, ABE = 1, and voltage is applied to the VBAUX pin.

DC Power for Primary Power Supply. When VCC is applied within the

normal limits, the device sis fully accessible and data can be written and

read. When VCC is below VPF reads and writes are inhibited.

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