Rainbow Electronics DS14287 - Manual (Page 2)

DS14285/DS14287
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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 - Interrupt Request Output
SQW - Square Wave Output
V
CC
- +5V Supply
GND - Ground
V
CCO
- RAM Power Supply Output
CEI - RAM Chip Enable In
CEO - RAM Chip Enable Out
X1, X2 - 32.768 kHz Crystal Connections
V
BAT
- +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.