DS14285 Datasheet, PDF (2/25 Pages) Dallas Semiconductor – Real Time Clock with NV RAM Control

DS14285/DS14287
ORDERING INFORMATION
DS14285
RTC Chip; 24-pin DIP
DS14285N
RTC Chip; 24-pin DIP; Industrial Temp Range
DS14285S
RTC Chip; 24-pin SOIC
DS14285SN
RTC Chip; 24-pin SOIC; Industrial Temp Range
DS14285Q
RTC Chip; 28-pin PLCC
DS14285QN
RTC Chip; 28-pin PLCC; Industrial Temp Range
DS14287
RTC Module; 24-pin DIP
PIN DESCRIPTION
AD0-AD7 - Multiplexed Address/Data Bus
NC
- No Connection
MOT
- Bus Type Select (DS14285Q only)
CS
- Chip Select
AS
- Address Strobe
R/ W
- Read/Write Input
DS
- Data Strobe
RESET
- Reset Input
IRQ
SQW
V_CC
GND
V_CCO
- Interrupt Request Output
- Square Wave Output
- +5V Supply
- Ground
- RAM Power Supply Output
CEI
- RAM Chip Enable In
CEO
X1, X2
V_BAT
- RAM Chip Enable Out
- 32.768 kHz Crystal Connections
- +3V Battery Input
DESCRIPTION
The DS14285/DS14287 Real Time Clock with NVRAM Control provides the industry standard DS1287
clock function with the additional feature of providing nonvolatile control for an external SRAM.
Functions include a nonvolatile time-of-day clock, alarm, 100-year calendar, programmable interrupt,
square wave generator, and 114 bytes of nonvolatile static RAM. For the DS14287 a lithium energy
source, quartz crystal, and write protection circuitry are contained within a 24-pin dual in-line package.
The DS14285 requires an external quartz crystal connected to the X1 and X2 pins as well as an external
energy source connected to the V_BAT pin. A standard 32.768 kHz quartz crystal can be directly connected
to the DS14285 via pins 1 and 2 (X1, X2). The crystal selected for use should have a specified load
capacitance (C_L) of 6 pF. For more information on crystal selection and crystal layout considerations,
please consult Application Note 58, “Crystal Considerations with Dallas Real-time Clocks.”
The DS14285/DS14287 uses its backup energy source and battery-backup controller to make a standard
CMOS static RAM nonvolatile during power-fail conditions. During power fail, the DS14285/DS14287
automatically write-protects the external SRAM and provides a V_CC output sourced from its internal
battery.
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