DS1670 datasheet(3/17 Pages) DALLAS

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DS1670

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CS (Chip Select) - The Chip Select signal must be asserted high during a read or a write for

communication over the 3-wire serial interface. CS had an internal 40k ohm pull down resistor.

VCCO (External SRAM Power Supply Output) - This pin is internally connected to VCC when VCC is

within nominal limits. However, during power fail VCCO is internally connected to the VBAT pin.

Switchover occurs when VCC drops below the lower of VBAT or 2.7 volts.

INT (Interrupt Output) - The INT pin is an active high output of the DS1670 that can be used as an

interrupt input to a microprocessor. The INT output remains high as long as the status bit causing the

interrupt is present and the corresponding interrupt-enable bit is set. The INT pin operates when the

DS1670 is powered by VCC or VBAT.

CEI

(RAM Chip Enable In) - CEI must be driven low to enable the external RAM.

BLE

(Byte Low Enable input) - This pin when driven low activates the CEOL output if CEI is also

driven low.

BHE

(Byte High Enable input) - This pin when driven low activates the CEOH output if CEI is also

driven low.

CEOL

(RAM Chip Enable Out Low) - Chip enable output for low order SRAM byte.

CEOH

(RAM Chip Enable Out High) - Chip enable output for high order SRAM byte.

(Strobe Input) - The Strobe input pin is used in conjunction with the watchdog timer. If the ST pin

is not driven low within the watchdog time period, the RST pin is driven low.

RST

(Reset) - The RST pin functions as a microprocessor reset signal. This pin is driven low 1) when

VCC is outside of nominal limits; 2) when the watchdog timer has “timed out”; 3) during the power up

reset period; and 4) in response to a pushbutton reset. The RST pin also functions as a pushbutton reset

input. When the RST pin is driven low, the signal is debounced and timed such that a RST signal of at

least 250 ms is generated. This pin has an open drain output with an internal 47 k

Ω pull-up resistor.

AIN0, AIN1, AIN2 (Analog Inputs) - These pins are the three analog inputs for the 3-channel analog-to-

digital converter.

X1, X2 - Connections for a standard 32.768 kHz quartz crystal. For greatest accuracy, the DS1670 must

be used with a crystal that has a specified load capacitance of 6 pF. 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.

For more information on crystal selection and crystal layout considerations, please consult

Application Note 58, “Crystal Considerations with Dallas Real Time Clocks.”

The DS1670 will not function without a crystal.

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