DS1673 Datasheet, PDF (3/18 Pages) Dallas Semiconductor – Portable System Controller

DS1673
PIN DESCRIPTION
PIN NAME
FUNCTION
1
V_BAT Battery Input for Standard 3V Lithium Cell or Other Energy Source
External SRAM Power Supply Output. This pin is internally connected to V_CC when
2
V_CCO V_CC is within nominal limits. However, during power-fail V_CCO is internally connected
to the V_BAT pin. Switchover occurs when V_CC drops below V_CCSW.
3
SCLK Serial Clock Input. Used to synchronize data movement on the serial interface.
4
I/O Data Input/Output. This pin is the bidirectional data pin for the 3-wire interface.
5
CS
Chip Select. Must be asserted high during a read or a write for communication over the
3-wire serial interface. CS has an internal 40kW pulldown resistor.
6
CEI RAM Chip-Enable In. Must be driven low to enable the external RAM.
7
CEOL ^{RAM Chip-Enable Out Low. Active-low chip-enable output for low-order SRAM}
byte.
8
CEOH
RAM Chip-Enable Out High. Active-low chip-enable output for high-order SRAM
byte.
Interrupt Output. This pin is an active-high output that can be used as an interrupt
9
INT
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 DS1673 is powered by V_CC or V_BAT.
10
GND Ground. DC power is provided to the device on this pin.
11
BHE
Byte High-Enable Input. This pin when driven low activates the CEOH output if CEI
is also driven low.
12
BLE
Byte Low-Enable Input. This pin when driven low activates the CEOL output if CEI is
also driven low.
Active-Low Reset. The RST pin functions as a microprocessor reset signal. This pin is
driven low 1) when V_CC is outside of nominal limits; 2) when the watchdog timer has
13
RST
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 250ms
is generated. This pin has an open-drain output with an internal 47kW pullup resistor.
14,
15, 16
AIN2,
AIN1,
AIN0
Analog Inputs. These pins are the three analog inputs for the 3-channel ADC.
17, 18
X2, X1
Connections for Standard 32.768kHz Quartz Crystal. For greatest accuracy, the
DS1673 must be used with a crystal that has a specified load capacitance of 6pF. 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, refer to Application
Note 58: Crystal Considerations with Dallas Real Time Clocks. The DS1673 does not
function without a crystal.
19
V_CC +3.0V or +5.0V Input DC Power
20
ST
Active-Low Strobe Input. The strobe input pin is used with the watchdog timer. If the
ST pin is not driven low within the watchdog time period, the RST pin is driven low.
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