Rainbow Electronics DS1670 User Manual

Page 3

DS1670

3 of 17

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.

CCO

(External SRAM Power Supply Output) - This pin is internally connected to V

when V

within nominal limits. However, during power fail V

CCO

is internally connected to the V

BAT

pin.

Switchover occurs when V

drops below the lower of V

BAT

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 V

or V

BAT

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

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

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.