DS1251Y
DS1251Y
4096K NV SRAM with Phantom Clock
FEATURES
PIN ASSIGNMENT
A18/RST
A16
A14
A12
A7
A6
A5
A4
A3
A2
A1
A0
DQ0
DQ1
DQ2
GND
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
V
CC
A15
A17
WE
A13
A8
A9
A11
OE
A10
CE
DQ7
DQ6
DQ5
DQ4
DQ3
•
Real time clock keeps track of hundredths of seconds,
minutes, hours, days, date of the month, months, and
years
•
512K x 8 NV SRAM directly replaces volatile static
RAM or EEPROM
•
Embedded lithium energy cell maintains calendar op-
eration and retains RAM data
•
Watch function is transparent to RAM operation
•
Month and year determine the number of days in each
month; valid up to 2100
•
Standard 32–pin JEDEC pinout
•
Full 10% operating range
•
Operating temperature range 0°C to 70°C
•
Accuracy is better than
±1
minute/month @ 25°C
•
Over
10 years of data retention in the absence of
power
32–PIN ENCAPSULATED PACKAGE
740 MIL FLUSH
PIN DESCRIPTION
A
0
–A
18
CE
GND
DQ
0
–DQ
7
V
CC
WE
OE
RST
–
–
–
–
–
–
–
–
Address Inputs
Chip Enable
Ground
Data In/Data Out
Power (+5V)
Write Enable
Output Enable
Reset
•
Available in 120 ns and 150 ns access time
ORDERING INFORMATION
DS1251Y–120
DS1251Y–150
120 ns access
150 ns access
DESCRIPTION
The DS1251Y 4096K NV SRAM with Phantom Clock is
a fully static nonvolatile RAM (organized as 512K words
by 8 bits) with a built–in real time clock. The DS1251Y
has a self–contained lithium energy source and control
circuitry which constantly monitors V
CC
for an out–of–
tolerance condition. When such a condition occurs, the
lithium energy source is automatically switched on and
write protection is unconditionally enabled to prevent
garbled data in both the memory and real time clock.
The Phantom Clock provides timekeeping information
including hundredths of seconds, seconds, minutes,
hours, day, date, month, and year information. The date
at the end of the month is automatically adjusted for
months with less than 31 days, including correction for
leap years. The Phantom Clock operates in either
24–hour or 12–hour format with an AM/PM indicator.
ECopyright
1997 by Dallas Semiconductor Corporation.
All Rights Reserved. For important information regarding
patents and other intellectual property rights, please refer to
Dallas Semiconductor data books.
032697 1/12
DALLAS [ DALLAS SEMICONDUCTOR ]
